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#include "bits/stdc++.h"

using namespace std;
#define PB push_back
#define LL long long
#define int LL
#define FOR(i,a,b) for (int i = (a); i <= (b); i++)
#define FORD(i,a,b) for (int i = (a); i >= (b); i--)
#define REP(i,n) FOR(i,0,(int)(n)-1)
#define st first
#define nd second
#define ALL(x) (x).begin(), (x).end()
#define SZ(x) ((int)(x).size())
#define VI vector<int>
#define PII pair<int,int>
#define LD long double

template<class C> void mini(C& a4, C b4) { a4 = min(a4, b4); }
template<class C> void maxi(C& a4, C b4) { a4 = max(a4, b4); }

template<class TH> void _dbg(const char *sdbg, TH h){cerr<<sdbg<<"="<<h<<"\n";}
template<class TH, class... TA> void _dbg(const char *sdbg, TH h, TA... a) {
  while(*sdbg!=',')cerr<<*sdbg++;cerr<<"="<<h<<","; _dbg(sdbg+1, a...);
}

template<class T> ostream &operator<<(ostream &os, vector<T> V){
  os<<"[";for(auto vv:V)os<<vv<<",";return os<<"]";
} 

template<class L, class R> ostream &operator<<(ostream &os, pair<L,R> P) {
  return os << "(" << P.st << "," << P.nd << ")";
}


#ifdef LOCAL
#define debug(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#else
#define debug(...) (__VA_ARGS__)
#define cerr if(0)cout
#endif


// halfplanes_online
#define X real()
#define Y imag()
typedef complex<LL> P;

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 (P const &A, P 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;}
int cross_prod(P a, P b){
  return (conj(a) * b).Y;
}
inline bool rown(line a, line b) {return wek(a,b) == 0;}
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;
    }
};

const LD EPS = 1e-12;

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]) && weaker(res[0], -res[1])<0) 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;
    }
};

template <typename T> int sgn(T val) {
  return (T(0) < val) - (val < T(0));
}

int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int n;
  cin>>n;
  vector<pair<P,P>> inp(n);
  REP(i, n){
    int x1, y1, x2, y2;
    cin>>x1>>y1>>x2>>y2;
    inp[i] = {{x1,y1}, {x2,y2}};
  }
  przeciecie_polplaszczyzn pp;
  REP(j, n){
    for(P p1: {inp[j].st, inp[j].nd}){
      REP(i, j){
        for(P p2: {inp[i].st, inp[i].nd}){
          for(pair<P,P> l: {pair<P,P>{p1, p2}, pair<P,P>{p2, p1}}){
            //debug(l.st, l.nd);
            REP(k, n){
              if(i == k || j == k)
                continue;
              int c1 = cross_prod(l.nd - l.st, inp[k].st - l.st);
              int c2 = cross_prod(l.nd - l.st, inp[k].nd - l.st);
              //debug(inp[k].st, inp[k].nd, c1, c2);
              if(c1 < 0 && c2 < 0){
                goto nxt;
              }
            }
            pp.add(line(l.st, l.nd));
            //debug(pp.type());
nxt:;
          }
        }
      }
    }
  }
  if(pp.type() != 5){
    cout<<0<<"\n";
    return 0;
  }
  debug(pp.S.size());
  auto it = pp.S.begin();
  auto it2 = ++pp.S.begin();
  vector<complex<LD>> pts;
  pts.reserve(pp.S.size());
  REP(i, SZ(pp.S)){
    debug(prosta_prosta(*it, *it2));
    pts.push_back(prosta_prosta(*it, *it2));
    it = pp.next(it);
    it2 = pp.next(it2);
  }
  LD pole = 0;
  REP(i, SZ(pts)){
    int ni = (i + 1) % SZ(pts);
    complex<LD> p1 = pts[i], p2 = pts[ni];
    pole += (p1.Y + p2.Y) * (p2.X - p1.X);
  }
  pole /= 2;
  pole = abs(pole);
  cout<<fixed<<setprecision(15);
  cout<<pole<<"\n";
}