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#include <bits/stdc++.h>
using namespace std;

// Przepraszam za brzydki kod : (

typedef long double LL;
typedef long double LD;
typedef pair<int,int> PII;
#define MP make_pair
#define FOR(v,p,k) for(int v=p;v<=k;++v)
#define FORD(v,p,k) for(int v=p;v>=k;--v)
#define REP(i,n) for(int i=0;i<(n);++i)
#define VAR(v,i) __typeof(i) v=(i)
#define FOREACH(i,c) for(VAR(i,(c).begin());i!=(c).end();++i)
#define PB push_back
#define ST first
#define ND second
#define SZ(x) (int)x.size()
#define ALL(c) c.begin(),c.end()

// Kod pożyczony z biblioteczki UW0:
// https://github.com/mareksom/acmlib/blob/master/code/kamil/halfplanes.cpp
// halfplanes_online

#define sim template < class c
#define ris return * this
#define dor > debug & operator <<
#define eni(x) sim > typename \
  enable_if<sizeof dud<c>(0) x 1, debug&>::type operator<<(c i) {
sim > struct rge { c b, e; };
sim > rge<c> range(c i, c j) { return rge<c>{i, j}; }
sim > auto dud(c* x) -> decltype(cerr << *x, 0);
sim > char dud(...);
struct debug {
#ifdef LOCAL
~debug() { cerr << endl; }
eni(!=) cerr << boolalpha << i; ris; }
eni(==) ris << range(begin(i), end(i)); }
sim, class b dor(pair < b, c > d) {
  ris << "(" << d.first << ", " << d.second << ")";
}
sim dor(rge<c> d) {
  *this << "[";
  for (auto it = d.b; it != d.e; ++it)
    *this << ", " + 2 * (it == d.b) << *it;
  ris << "]";
}
#else
sim dor(const c&) { ris; }
#endif
};
#define imie(...) " [" << #__VA_ARGS__ ": " << (__VA_ARGS__) << "] "

template<typename T> T K(T a) { return a * a; } // 'K(int)' may overflow!
typedef long double ll; // can be changed to 'long double'
typedef long double ld;
// const ld PI = 2 * acos(0);
const ld eps = 1e-12;
#pragma GCC diagnostic ignored "-Wnarrowing"
struct P {
	ll x, y;
	P operator + (P b) { return P{x + b.x, y + b.y}; }
	P operator - (P b) { return P{x - b.x, y - b.y}; }
	P operator * (ld/*ll*/ mul) { return P{x * mul, y * mul}; }
	P operator / (ld mul) { assert(mul); return P{x / mul, y / mul}; }
	ll operator * (P b) { return x * b.y - y * b.x; }
	ll dot(P b) { return x * b.x + y * b.y; }
	ld len() { return sqrt(K(x) + K(y)); }
	P scaleTo(ld to) { return *this * (to / len()); }
	ld dist(P & b) { return (*this - b).len(); }
	P rotate90() { return P{-y, x}; }
	ld angle() { return atan2(y, x); }
	P rotate(ld ang) {
		ld c = cos(ang), s = sin(ang);
		return P{x * c - y * s, x * s + y * c};
	}
	// '<' and 'below()' needed for Convex Hull
	bool operator < (P he) { return make_pair(x, y) < make_pair(he.x, he.y); }
	bool below(P a, P b) { return (b - a) * (*this - a) <= 0/*eps*/; } //INFO 1
	void write(string s) { cerr << "(" << x << ", " << y << ")" << s; }
	// Internal/External Similitude Center
	P apol_in(P b, ld ratio) { // ratio = dist()/he.dist()
		return (*this + b * ratio) / (1 + ratio);
	}
	P apol_out(P b, ld ratio) {
		return (*this - b * ratio) / (1 - ratio);
	}
	void print(debug & dd) const {
		dd << make_pair(x, y);
	}
};

/*   using debug()
ostream & operator << (ostream & dd, P p) {
	dd << "(" << p.x << ", " << p.y << ") ";
	return dd;
}
*/

debug & operator << (debug & dd, P p) {
	p.print(dd);
	return dd;
}

struct L2 {
	P one, two;
	// P p[2]; P & operator [](int i) { return p[i]; }
	// const P & operator [](int i) const { return p[i]; }
	P dir() { return two - one; }
	P normal() { return dir().rotate90(); }
	ld dist(P he) {
		return abs((he - one) * (he - two)) / one.dist(two);
	}
	ld segDist(P he) {
		// epsilon not needed, but it would work too
		if((he - two) * normal() < 0 && normal() * (he - one) < 0)
			return dist(he);
		return min(one.dist(he), two.dist(he));
	}
	P inter(L2 he) {
		P A = dir(), B = he.dir();
		ll den = A * B;
		assert(abs(den) > eps); // parallel, maybe equal
		return (A * (he.one * he.two) - B * (one * two)) * (1.0 / den);
		// https://en.wikipedia.org/wiki/Line-line_intersection
		// A = (x1*y2-y1*x2)*(x3-x4)-(x1-x2)*(x3*y4-y3*x4)
		// A'= (x1*y2-y1*x2)*(y3-y4)-(y1-y2)*(x3*y4-y3*x4)
		// B = (x1-x2)*(y3-y4)-(y1-y2)*(x3-x4)
		// return P{A / B, A' / B};
	}
	P project(P he) {
		P unit_normal = normal().scaleTo(1);
		return he + unit_normal * unit_normal.dot(one - he);
	}
	P reflect(P he) { return project(he) * 2 - he; }
	void print(debug & dd) const { dd << imie(one) << imie(two); }
	void write() { cerr << "L2{ "; one.write(", "); cerr << " }\n"; }
	// for CH: sort by slope; below() : change to L3 or compare 'x' of intersections
};
L2 toL2(ll a, ll b, ll c) {
	P first;
	if(abs(b) > eps) first = P{0, (ld) -c / b};
	else if(abs(a) > eps) first = P{(ld) -c / a, 0};
	else assert(false);
	return L2{first, first + P{b, -a}};
}

ll det(ll t[3][3]) { // for CH of lines Ax+By+C=0
	ll s = 0;
	for(int i = 0; i < 3; ++i)
		for(int j = i + 1, mul = 1; j != i + 3; ++j, mul -= 2)
			s += t[0][i] * t[1][j%3] * t[2][3-i-j%3] * mul;
	return s;
}

struct L3 {
	// a * x + b * y + c = 0, assert(b > 0 || (b == 0 && a > 0))
	ll a, b, c;
	L3 fix() { // <done>TODO, test it</done>
		assert(abs(b) > eps || abs(a) > eps);
		ll g = (b > eps || (abs(b) < eps && a > eps)) ? 1 : -1;
		// __gcd(x,0) is undef-beh, http://codeforces.com/blog/entry/13410
		// if(is_integral<ll>::value) g *= abs(__gcd(c, __gcd(a?b:a, a?a:b)));
		// if(is_floating_point<ll>::value) g *= sqrt(K(a) + K(b));
		return L3{a / g, b / g, c / g};
	}
	ld dist(P he) {
		return abs(a * he.x + b * he.y + c) / sqrt(K(a) + K(b));
	}
	P dir() { return P{b, -a}; }
	P normal() { return P{a, b}; } // equivalently: dir().rotate90()
	P project(P he) {
		ld den = K(a) + K(b); // non-integer because we need division
		return P{(b * (b * he.x - a * he.y) - a * c) / den,
				 (a * (a * he.y - b * he.x) - b * c) / den };
	}
	P reflect(P he) { return project(he) * 2 - he; }
	P inter(L3 he) {
		#define Q(i, j) (i * he.j - j * he.i)
		ll den = Q(a, b);
		assert(abs(den) > 1e-14); // parallel, maybe equal
		return P{Q(b, c), Q(c, a)} * (1.0 / den);
		#undef Q
	}
	bool operator < (L3 he) {
		// produces the order for finding an upper envelope
		// assert(b > 0 && he.b > 0);
		// a / b < he.a / he.b, ties: -c/b < ...
		if(abs(a * he.b - b * he.a) < eps) return b * he.c < c * he.b;
							// <done>test it</done>
		return a * he.b < b * he.a;
	}
	bool below(L3 A, L3 C) {
		ll t[3][3] = { {A.a,A.b,A.c}, {a,b,c}, {C.a,C.b,C.c} };
		return det(t) <= 0/*eps*/; // WARN1
	}
};
L3 toL3(P one, P two) {
	ll a = two.y - one.y;
	ll b = one.x - two.x;
	return L3{a, b, -(a * one.x + b * one.y)}.fix();
}

#define X real()
#define Y imag()
typedef complex<LL> Pu;


const LD EPS = 1e-10;

struct line {
    LL a,b,c;
    line(LL a_ = 0, LL b_ = 0, LL c_ = 0): a(a_), b(b_), c(c_) {} // <= 10^9
    line (Pu const &A, Pu const &B): a(A.Y-B.Y), b(B.X-A.X), c(A.X*B.Y-A.Y*B.X) {} //pts <= 10^6

    line operator - () const {return line(-a, -b, -c); }
    bool up() const { return a?(a<0):(b>0);}
};

inline LL wek(line const &a, line const &b) {return a.a*b.b-a.b*b.a;}
inline bool rown(line a, line b) {return abs(wek(a,b)) < EPS;}
inline bool pokr(line a, line b) {return rown(a,b) && a.a*b.c == b.a*a.c && a.b*b.c == b.b*a.c;}
inline bool podobne(line a, line b) {return rown(a,b) && a.up() == b.up();}

inline complex<LD> prosta_prosta(line a, line b) {
    LL det = wek(a,b);
    LL x =  -a.c*b.b+b.c*a.b;
    LL y =  -a.a*b.c+a.c*b.a;
    return complex<LD>(x,y)/(LD)det;
}

inline LL weaker (line a, line b) { // czy a jest slabsze niz b
    assert(rown(a,b));
    if (abs(a.a) > abs(a.b)) return a.c*abs(b.a) -  b.c*abs(a.a);
    else return a.c*abs(b.b) -  b.c*abs(a.b);
}

struct Comp {
    bool operator()(const line& a, const line& b) const {
        if (a.up() != b.up()) return a.up() > b.up();
        return wek(a,b) > 0;
    }
};


struct przeciecie_polplaszczyzn {
    bool empty, pek;
    set<line, Comp> S;
    typedef set<line, Comp>::iterator iter;

    przeciecie_polplaszczyzn() : empty(false), pek(false) {};

    iter next(iter it){return (++it == S.end() ? S.begin() : it);}
    iter prev(iter it){return (it == S.begin() ? --S.end() : --it);}

    bool hide(line a, line b, line c) {
        if (rown(a,b)) {
            if (weaker(a, -b) < 0) empty = true;
            return false; 
        }
        if (wek(a,b) < 0) swap(a,b);
        complex<LD> r = prosta_prosta(a,b);
        LD v = r.X * c.a + r.Y * c.b + c.c;
        if (wek(a,c) >=0  && wek(c,b) >=0 && v > -EPS) return true;
        if (wek(a,c) < 0  && wek(c,b) < 0) {
            if (v < -EPS) empty = true;
            else if (v < EPS) pek = true;
        }
        return false;
    }

    void add(line l) {
        if (empty) return;
        if (l.a == 0 && l.b == 0) {
            if (l.c < 0) empty = true;
            return;
        }
        iter it = S.lower_bound(l);
        //rownolegle
        if(it != S.end() && podobne(*it, l)) {
            if (weaker(l, *it)>=0) return;
            iter del = it;
            it = next(it);
            S.erase(del);
        }
        //*it>p
        if(SZ(S) >= 2 && it == S.end()) it = S.begin();
        while(SZ(S) >= 2 && hide(l, *next(it), *it)) {
            iter del = it;
            it = next(it);
            S.erase(del);
        }
        //*it<p
        if(SZ(S) >= 2) it = prev(it);
        while(SZ(S) >= 2 && hide(l, *prev(it), *it)) {
            iter del = it;
            it = prev(it);
            S.erase(del);
        }
        if(S.size() < 2 || !hide(*it, *next(it), l)) S.insert(l);
    }
    /*	 0 - puste	 1 - punkt	 2 - odcinek	 3 - półprosta	 4 - prosta
         5 - dodatnie (może nieskończone) pole (S.size() daje wowczas liczbę boków) */
    int type() {
        if(empty) return 0;
        if(SZ(S) <= 4){
            vector<line> res(ALL(S));
            if (SZ(res) == 2 && rown(res[0], res[1]) && abs(weaker(res[0], -res[1]))<EPS) return 0; 
            REP(i, SZ(res)) REP(j, i) if(pokr(res[i], res[j])) {
                if(SZ(res) == 2) return 4;
                if(SZ(res) == 3) return 3;
                if(SZ(res) == 4 && pokr(res[0], res[2]) && pokr(res[1], res[3])) return 1;
                return 2;
            }
            if(SZ(res) == 3 && pek) return 1;
        }
        return 5;
    }
};

// END OF LIB

bool operator == (P a, P b) {
	return a.x == b.x && a.y == b.y;
}

bool operator != (P a, P b) {
	return not (a == b);
}

ld dir_dist(L3 l, P he) {
	return (l.a * he.x + l.b * he.y + l.c) / sqrt(K(l.a) + K(l.b));
}

P jedn(P a) {
	return a.scaleTo(1.0);
}

L3 from_line(line l) {
	return L3({l.a, l.b, l.c});
}

// END OF HELP FUNS

vector<vector<P>> towers;

przeciecie_polplaszczyzn pp;

bool cosik = false;

void dorzuc(P a, P b) {
	line l1 = line({a.x, a.y}, {b.x, b.y});
	line l2 = line({b.x, b.y}, {a.x, a.y});
	L3 l3 = L3({l1.a, l1.b, l1.c});
	ld mniej = 1e9;
	ld wiecej = -1e9;
	int mniej_id = 0;
	int wiecej_id = 0;
	for (int i = 1; i < towers.size(); i ++) {
		ld ad = dir_dist(l3, towers[i][0]);
		ld bd = dir_dist(l3, towers[i][1]);
		if (ad * bd >= 0) {
			// This point is damn good
			if (ad < 0 || bd < 0) {
				mniej = min({mniej, max(ad, bd)});
				if (mniej == max(ad, bd)) mniej_id = i;
			}
			if (ad > 0 || bd > 0) {
				wiecej = max({wiecej, min(ad, bd)});
				if (wiecej == min(ad, bd)) wiecej_id = i;
			}
		}
	}
//	cerr << l1.up() << "\n";
	if (mniej <= 0) {
		P n = jedn(l3.normal()) * mniej;
		P a1 = a + n;
		P b1 = b + n;
		line x = line({a1.x, a1.y}, {b1.x, b1.y});
		if (abs(max(dir_dist(from_line(x), towers[mniej_id][0]), dir_dist(from_line(x), towers[mniej_id][1]))) > EPS) {
			a1 = a - n;
			b1 = b - n;
			x = line({a1.x, a1.y}, {b1.x, b1.y});
		}
//		cerr << x.a << " " << x.b << " " << x.c << "\n";
		pp.add(x);
		cosik = true;
	}
	if (wiecej >= 0) {
		P n = jedn(l3.normal()) * wiecej;
		P a1 = a + n;
		P b1 = b + n;
		line x = line({b1.x, b1.y}, {a1.x, a1.y});
		if (abs(max(dir_dist(from_line(x), towers[wiecej_id][0]), dir_dist(from_line(x), towers[wiecej_id][1]))) > EPS) {
			a1 = a - n;
			b1 = b - n;
			x = line({b1.x, b1.y}, {a1.x, a1.y});
		}
//		cerr << x.a << " " << x.b << " " << x.c << "\n";
		pp.add(x);
		cosik = true;
	}
//	cerr << mniej << "\n";
//	cerr << wiecej << "\n";
//	cerr << l1.a << " " << l1.b << " " << l1.c << "\n";
//	cerr << "{ "<< a.x << " " << a.y << "} \n";
	
//	cerr << "{ " << b.x << " " << b.y << "} \n";
//	line a3 = line(l1.a, l1.b, l1.c + wiecej * sqrt(K(l1.a) + K(l1.b)));
//	line b3 = line(l2.a, l2.b, l2.c - mniej * sqrt(K(l2.a) + K(l2.b))); 
//	if (wiecej >= 0) cerr << a3.a << " " << a3.b << " " << a3.c << "\n";
//	if (mniej <= 0) cerr << b3.a << " " << b3.b << " " << b3.c << "\n";
//	cout << pp.type() << "\n";
/*	if (pp.type() == 5) {
		cerr << "BEG OF S\n";
		for (line l : pp.S) {
			cerr << l.a <<" " << l.b << " " << l.c << "\n";
		}
		cerr <<"END OF S\n";
	}*/
}

int main() {
	ios_base::sync_with_stdio(false);
	cout << setprecision(16) << fixed;
	int n;
	cin >> n;
	towers.resize(1);
	for (int i = 1; i <= n; i ++) {
		int a, b, c, d;
		cin >> a >> b >> c >> d;
		P p1 = P({a, b});
		P p2 = P({c, d});
		towers.push_back({p1, p2});
	}
	for (int i = 1; i <= n; i ++) {
		for (int j = i + 1; j <= n; j ++) {
			for (P a : towers[i]) {
				for (P b : towers[j]) {
					if (a != b) {
						dorzuc(a, b);
					}
				}
			}
		}
	}
	LD result = 0;
	if (pp.type() != 5 || cosik == false) {
		cout << result << "\n";
		return 0;
	}
	if (pp.type() == 5) {
//		cerr << "BEG OF S\n";
		for (line l : pp.S) {
//			cerr << l.a <<" " << l.b << " " << l.c << "\n";
		}
//		cerr <<"END OF S\n";
	}
//	cout << "LOOOOL\n";
	line last = *pp.S.rbegin();
	vector<P> polygon;
	for (line l : pp.S) {
		polygon.push_back(from_line(last).inter(from_line(l)));
		last = l;
	}
//	cerr << polygon.size() << "\n";
//	cerr << "POLYGON\n";
	for (P p : polygon) {
//		cerr << p.x << " " << p.y << "\n";
	}
	for (int i = 1; i < polygon.size() - 1; i ++) {
		result += (polygon[i] - polygon[0]) * (polygon[i+1] - polygon[0]);
	}
	cout << abs(result) / 2 <<"\n";
}