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#include <cstdio>
#include <algorithm>
#include <vector>
#include <cmath>
typedef long long LL;
typedef long double LD;

struct vec2 {
	LD x, y;
};

struct ivec2 {
	int x, y;
};

ivec2 operator-(ivec2 u, ivec2 v) {
	return ivec2{u.x-v.x, u.y-v.y};
}

LD det(vec2 u, vec2 v) {
	return u.x*v.y - u.y*v.x;
}

int det(ivec2 u, ivec2 v) {
	return u.x*v.y - u.y*v.x;
}


// Ax + By + C > 0
struct halfplane {
	int A, B, C;
	//u -> v z prawej
	halfplane(ivec2 u, ivec2 v) {
		ivec2 w = u-v;
		A = w.y;
		B = -w.x;
		C = - A*u.x - B*u.y;
	}
};

vec2 intersection(halfplane h1, halfplane h2) {
	LD d = det(ivec2{h1.A, h2.A}, ivec2{h1.B, h2.B});
	LD x = LD(h2.B)*h1.C - LD(h1.B)*h2.C;
	LD y = LD(h1.A)*h2.C - LD(h2.A)*h1.C;
	return vec2{-x/d, -y/d};
}

bool inside(halfplane h, vec2 v) {
	return h.A*v.x + h.B*v.y + h.C > 0;
}


void radial_sort(std::vector<halfplane>& hp) {

	auto mid = std::partition(hp.begin(), hp.end(), [](halfplane h) {
		if(h.B != 0) return h.B < 0;
		return h.A > 0;
	});

	auto srt_cmp = [](halfplane h1, halfplane h2) {
		int d = det(ivec2{h1.A, h2.A}, ivec2{h1.B, h2.B});
		if(d != 0) return d < 0;

		LD a1 = sqrt(h1.A*h1.A + h1.B*h1.B);
		LD a2 = sqrt(h2.A*h2.A + h2.B*h2.B);
		return h1.C/a1 < h2.C/a2;
	};

	std::sort(hp.begin(), mid, srt_cmp);
	std::sort(mid, hp.end(), srt_cmp);
	auto new_end = std::unique(hp.begin(), hp.end(), [](halfplane h1, halfplane h2) {
		return det(ivec2{h1.A, h2.A}, ivec2{h1.B, h2.B}) == 0;
	});
	hp.erase(new_end, hp.end());
}

LD area(std::vector<halfplane> hp) {
	radial_sort(hp);


	std::vector<std::pair<vec2, int>> stack = {{vec2{0, 0}, 0}};

	int i = 1;
	for(; det(ivec2{hp[0].A, hp[0].B}, ivec2{hp[i].A, hp[i].B}) <= 0; i++) {
		while(stack.size() > 1 && !inside(hp[i], stack.back().first))
			stack.pop_back();

		stack.emplace_back(intersection(hp[stack.back().second], hp[i]), i);
	}

	auto beg = 0;
	bool at_inf = true;
	
	for(; i < int(hp.size()); i++) {

		if(!at_inf && inside(hp[i], stack[beg].first)) continue;
		at_inf = false;

		while(beg+1 < int(stack.size()) && !inside(hp[i], stack[beg+1].first))
			beg++;
		if(beg+1 == int(stack.size())) return 0;

		stack[beg].first = intersection(hp[i], hp[stack[beg].second]);

		while(!inside(hp[i], stack.back().first))
			stack.pop_back();

		stack.emplace_back(intersection(hp[i], hp[stack.back().second]), i);
	}

	LD area = 0.0;

	for(int j = beg+1; j < int(stack.size()); j++)
		area += det(stack[j].first, stack[j-1].first);

	area += det(stack[beg].first, stack.back().first);

	return area * 0.5;
}

ivec2 points[2][100];

int main() {
	int n;
	scanf("%i", &n);
	for(int i = 0; i < n; i++)
		scanf("%i%i%i%i", &points[0][i].x, &points[0][i].y, &points[1][i].x, &points[1][i].y);

	std::vector<halfplane> hp;
	for(int i = 0; i < n; i++)
		for(int j = i+1; j < n; j++) {
			
			for(int ind1 = 0; ind1 < 2; ind1++)
			for(int ind2 = 0; ind2 < 2; ind2++) {
				ivec2 u = points[ind1][i];
				ivec2 v = points[ind2][j];
				bool allleft = true;
				bool allright = true;

				for(int k = 0; k < n; k++) {
					if(k == i || k == j) continue;
					int d0 = det(v-u, points[0][k]-u);
					int d1 = det(v-u, points[1][k]-u);

					if(d0 < 0 && d1 < 0) allright = false;
					if(d0 > 0 && d1 > 0) allleft = false;
				}

				if(allright) hp.emplace_back(u, v);
				if(allleft)  hp.emplace_back(v, u);
			}
		}

	printf("%.13Lf\n", area(hp));
}