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#define _USE_MATH_DEFINES/////////////////////////////////////////////////////
#include <bits/stdc++.h>//////////////////////////////////////////////////////
#ifdef LOC////////////////////////////////////////////////////////////////////
#include "debuglib.h"/////////////////////////////////////////////////////////
#else/////////////////////////////////////////////////////////////////////////
#define deb(...)//////////////////////////////////////////////////////////////
#define DBP(...)//////////////////////////////////////////////////////////////
#endif////////////////////////////////////////////////////////////////////////
#define x first///////////////////////////////////////////////////////////////
#define y second//////////////////////////////////////////////////////////////
#define mp make_pair//////////////////////////////////////////////////////////
#define pb push_back//////////////////////////////////////////////////////////
#define sz(x)int((x).size())//////////////////////////////////////////////////
#define each(a,x)for(auto&a:(x))//////////////////////////////////////////////
#define all(x)(x).begin(),(x).end()///////////////////////////////////////////
#define rep(i,b,e)for(int i=(b);i<(e);i++)////////////////////////////////////
using namespace std;using namespace rel_ops;using ll=int64_t;using Pii=pair///
<int,int>;using ull=uint64_t;using Vi=vector<int>;void run();int main(){cin.//
sync_with_stdio(0);cin.tie(0);cout<<fixed<<setprecision(13);run();return 0;}//
//--------------------------------------------------------------------------//

using dbl = long double;
constexpr dbl EPS = 1e-9;

int cmp(dbl a, dbl b, dbl eps=EPS) { return (a>b+eps) - (a+eps<b); }

template<class T, class S> struct bvec2 {
	T x, y;
	S operator+(S r) const {return{x+r.x,y+r.y};}
	S operator-(S r) const {return{x-r.x,y-r.y};}
	S operator*(T r) const { return {x*r, y*r}; }
	S operator/(T r) const { return {x/r, y/r}; }
	S operator-()    const { return {-x, -y};   }
	T dot(S r)   const { return x*r.x+y*r.y; }
	T cross(S r) const { return x*r.y-y*r.x; }
	T len2()     const { return x*x + y*y; }
	dbl len()    const { return sqrt(len2()); }
	S perp()     const { return {-y,x}; } //90deg
	pair<T, T> yxPair() const { return mp(y,x); }
};

struct vec2d : bvec2<dbl, vec2d> {
	vec2d() : bvec2{0, 0} {}
	vec2d(dbl a, dbl b) : bvec2{a, b} {}
	vec2d unit() const { return *this/len(); }
	bool operator==(vec2d r) const { return !cmp(x, r.x) && !cmp(y, r.y); }

	int cmpAngle(vec2d r) const {
		int u = upper() - r.upper();
		return u ? u : cmp(cross(r), 0);
	}

	bool upper() const {
		int t = cmp(y, 0);
		return t > 0 || (t == 0 && cmp(x, 0) >= 0);
	}
};

template<class T, class P, class S>
struct bline2 { // norm*point == off
	P norm; // Normal vector [A; B]
	T off;  // Offset (C parameter of equation)
	static S through(P a, P b) { return { (b-a).perp(), b.cross(a) }; }
};

struct line2d : bline2<dbl, vec2d, line2d> {
	line2d() : bline2{{}, 0} {}
	line2d(vec2d n, dbl c) : bline2{n, c} {}
	int side(vec2d a) { return cmp(norm.dot(a), off); }

	bool intersect(line2d a, vec2d& out) {
		dbl d = norm.cross(a.norm);
		if (cmp(d, 0) == 0) return false;
		out = (norm*a.off-a.norm*off).perp() / d;
		return true;
	}

	bool lower(const line2d& r) const {
		return off*r.norm.len() < r.off*norm.len();
	}

	bool operator<(const line2d& r) const {
		return norm.cmpAngle(r.norm) > 0;
	}
};

using vec2 = vec2d;
using line2 = line2d;

// ---

struct HalfLine {
	line2 line;
	vec2 begin;
	int id;
};

vector<pair<vec2, vec2>> points;
vector<line2> halfPlanes;

void answer(dbl ans) {
	cout << ans << endl;
	exit(0);
}

void check(vec2 from, vec2 to) {
	line2 line = line2::through(from, to);
	bool negHalf = 0, posHalf = 0;

	each(p, points) {
		int a = line.side(p.x), b = line.side(p.y);
		if (a < 0 && b < 0) negHalf = 1;
		else if (a > 0 && b > 0) posHalf = 1;
	}

	if (!negHalf && !posHalf) {
		answer(0);
	}

	if (negHalf == posHalf) return;

	if (posHalf) {
		line.norm = -line.norm;
		line.off = -line.off;
	} else {
		swap(from, to);
	}

	halfPlanes.pb(line);
}

void run() {
	int n; cin >> n;
	points.resize(n);
	each(p, points) cin >> p.x.x >> p.x.y >> p.y.x >> p.y.y;

	rep(i, 0, n) rep(j, i+1, n) {
		check(points[i].x, points[j].x);
		check(points[i].x, points[j].y);
		check(points[i].y, points[j].x);
		check(points[i].y, points[j].y);
	}

	if (halfPlanes.empty()) answer(0);
	sort(all(halfPlanes));

	vector<HalfLine> inter;

	rep(step, 0, 2) {
		rep(i, 0, sz(halfPlanes)) {
			auto& cur = halfPlanes[i];
			HalfLine half{cur, {}, i};
			bool ok = 1;

			while (!inter.empty()) {
				auto& top = inter.back();

				if (!cur.intersect(top.line, half.begin)) {
					if (top.line.lower(cur)) {
						ok = 0;
						break;
					}
					inter.pop_back();
					continue;
				}

				if (sz(inter) <= 1) break;

				dbl curPos = half.begin.cross(top.line.norm);
				dbl topPos = top.begin.cross(top.line.norm);

				if (cmp(topPos, curPos) > 0) break;
				inter.pop_back();
			}

			if (ok) inter.pb(half);
		}
	}

	Vi counts(sz(halfPlanes));
	vector<vec2> border;

	each(h, inter) {
		counts[h.id]++;
		if (counts[h.id] == 2) {
			border.pb(h.begin);
		}
	}

	dbl area = 0;

	rep(i, 2, sz(border)) {
		vec2 a = border[i] - border[0];
		vec2 b = border[i-1] - border[0];
		area += abs(a.cross(b) / 2);
	}

	cout << area << endl;
}