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//#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <vector>
#include <cmath>

using namespace std;

int n, mag[100][4], pun[10][2], nr1, nr2, nr3, to[100], nrp, si;
long double dob1, dob2, dob3, wyn = 0;;
vector <long double>prost[4];
vector <int>kom;

int portan(int x1, int y1, int x2, int y2)
{
	if (y1 * x2 == y2 * x1)return 0;
	if (y1 * x2 > y2 * x1)return 1;
	return 2;
}

int sorwek(int a1, int a2, int b1, int b2, int c1, int c2)
{
	//printf("%d %d %d %d %d %d\n\n", a1, a2, b1, b2, c1, c2);
	if (a1 == 0)
	{
		if (a2 > 0)
		{
			if (b1 > 0 && c1 < 0)return 2;
			if (b1 < 0 && c1 > 0)return 3;
			if (portan(b1, b2, c1, c2) == 0)
			{
				if (b1*b1 + b2 * b2 < c1*c1 + c2 * c2)
				{
					return 2;
				}
				return 3;
			}
			if (portan(b1, b2, c1, c2) == 1)return 3;
			return 2;
		}
		else
		{
			if (b1 > 0 && c1 < 0)return 3;
			if (b1 < 0 && c1 > 0)return 2;
			if (portan(b1, b2, c1, c2) == 0)
			{
				if (b1*b1 + b2 * b2 < c1*c1 + c2 * c2)
				{
					return 2;
				}
				return 3;
			}
			if (portan(b1, b2, c1, c2) == 1)return 2;
			return 3;
		}
	}
	if (a1 < 0)
	{
		if (b1 == 0 && c1 == 0)
		{
			if (b2*c2 > 0)
			{
				if (b2*b2 > c2*c2)return 3;
				else return 2;
			}
			if (b2 > 0) return 2;
			return 3;
		}
		if (b1 == 0)
		{
			if (b2 > 0)
			{
				if (c1 > 0)return 2;
				if (portan(a1, a2, c1, c2) == 0)return 2;
				if (portan(a1, a2, c1, c2) == 1)return 3;
				return 2;
			}
			if (b2 < 0)
			{
				if (c1 > 0)return 3;
				if (portan(a1, a2, c1, c2) == 0)return 2;
				if (portan(a1, a2, c1, c2) == 1)return 3;
				return 2;
			}
		}
		if (c1 == 0)
		{

			if (c2 > 0)
			{
				if (b1 > 0)return 3;
				if (portan(a1, a2, b1, b2) == 0)return 3;
				if (portan(a1, a2, b1, b2) == 1)return 2;
				return 3;
			}
			if (c2 < 0)
			{
				if (b1 > 0)return 2;
				if (portan(a1, a2, b1, b2) == 0)return 3;
				if (portan(a1, a2, b1, b2) == 1)return 2;
				return 3;
			}
		}
	}
	if (a1 > 0)
	{
		if (b1 == 0 && c1 == 0)
		{
			if (b2*c2 > 0)
			{
				if (b2*b2 > c2*c2)return 3;
				else return 2;
			}
			if (b2 > 0) return 3;
			return 2;
		}

		if (b1 == 0)
		{
			if (b2 > 0)
			{
				if (c1 > 0)return 3;
				if (portan(a1, a2, c1, c2) == 0)return 2;
				if (portan(a1, a2, c1, c2) == 1)return 3;
				return 2;
			}
			if (b2 < 0)
			{
				if (c1 > 0)return 2;
				if (portan(a1, a2, c1, c2) == 0)return 2;
				if (portan(a1, a2, c1, c2) == 1)return 3;
				return 2;
			}
		}
		if (c1 == 0)
		{

			if (c2 > 0)
			{
				if (b1 > 0)return 2;
				if (portan(a1, a2, b1, b2) == 0)return 3;
				if (portan(a1, a2, b1, b2) == 1)return 2;
				return 3;
			}
			if (c2 < 0)
			{
				if (b1 > 0)return 3;
				if (portan(a1, a2, b1, b2) == 0)return 3;
				if (portan(a1, a2, b1, b2) == 1)return 2;
				return 3;
			}
		}
	}
	if (b1*c1 > 0)
	{
		if (a1*b1 > 0)
		{
			if (portan(a1, a2, b1, b2) == 0)return 3;
			if (portan(a1, a2, c1, c2) == 0)return 2;
			if (portan(a1, a2, b1, b2) == 1 && portan(a1, a2, c1, c2) == 2)return 2;
			if (portan(a1, a2, b1, b2) == 2 && portan(a1, a2, c1, c2) == 1)return 3;
			if (portan(b1, b2, c1, c2) == 0)
			{
				if (b1*b1 < c1*c1)return 2;
				return 3;
			}
			if (portan(b1, b2, c1, c2) == 1)return 2;
			return 3;
		}
		if (portan(b1, b2, c1, c2) == 0)
		{
			if (b1*b1 < c1*c1)return 2;
			return 3;
		}
		if (portan(b1, b2, c1, c2) == 1)return 2;
		return 3;
	}
	if (a1*b1 > 0)
	{
		if (portan(a1, a2, b1, b2) == 0)return 3;
		if (portan(a1, a2, b1, b2) == 1)return 2;
		return 3;
	}
	if (portan(a1, a2, c1, c2) == 0)return 2;
	if (portan(a1, a2, c1, c2) == 1)return 3;
	return 2;
}

long double polet(long double x1, long double y1, long double x2, long double y2, long double x3, long double y3)
{
	long double a, b, c, p;
	a = (x2 - x1) * (x2 - x1) + (y2 - y1) * (y2 - y1);
	b = (x3 - x2) * (x3 - x2) + (y3 - y2) * (y3 - y2);
	c = (x3 - x1) * (x3 - x1) + (y3 - y1) * (y3 - y1);
	a = sqrt(a);
	b = sqrt(b);
	c = sqrt(c);
	p = a + b + c;
	p /= 2;
	p = p * (p - a)*(p - b)*(p - c);
	p = sqrt(p);
	return p;
}

int main()
{
	scanf("%d", &n);
	for (int i = 0; i < n; i++)
	{
		scanf("%d%d%d%d", &mag[i][0], &mag[i][1], &mag[i][2], &mag[i][3]);
	}
	for (int i = 0; i < n; i++)to[i] = 0;
	//printf("mag nr 2\n%d %d\n%d %d\n", mag[1][0], mag[1][1], mag[1][2], mag[1][3]);
	pun[0][0] = mag[0][0];
	pun[0][1] = mag[0][1];
	pun[1][0] = mag[0][2];
	pun[1][1] = mag[0][3];
	if (pun[0][0] == pun[1][0] && pun[0][1] < pun[1][1])
	{
		pun[0][0] = pun[1][0];
		pun[0][1] = pun[1][1];
	}
	if (pun[0][0] < pun[1][0])
	{
		pun[0][0] = pun[1][0];
		pun[0][1] = pun[1][1];
	}
	nr1 = 0;
	for (int i = 1; i < n; i++)
	{
		pun[2][0] = mag[i][0];
		pun[2][1] = mag[i][1];
		pun[3][0] = mag[i][2];
		pun[3][1] = mag[i][3];


		if (pun[2][0] == pun[3][0] && pun[2][1] < pun[3][1])
		{
			pun[2][0] = pun[3][0];
			pun[2][1] = pun[3][1];
		}
		if (pun[2][0] < pun[3][0])
		{
			pun[2][0] = pun[3][0];
			pun[2][1] = pun[3][1];
		}


		if (pun[0][0] == pun[2][0] && pun[0][1] > pun[2][1])
		{
			pun[0][0] = pun[2][0];
			pun[0][1] = pun[2][1];
			nr1 = i;
		}
		if (pun[0][0] > pun[2][0])
		{
			pun[0][0] = pun[2][0];
			pun[0][1] = pun[2][1];
			nr1 = i;
		}
	}
	nrp = nr1;


	pun[0][0] = mag[nr1][0];
	pun[0][1] = mag[nr1][1];
	pun[2][0] = pun[0][0] - 1;
	pun[2][1] = pun[0][1];
	for (int i = 0; i < n; i++)
	{
		if (i == nr1)continue;
		if (to[i] == 1)continue;
		if (sorwek(-502, 0, mag[i][0] - pun[0][0], mag[i][1] - pun[0][1], mag[i][2] - pun[0][0], mag[i][3] - pun[0][1]) == 2)
		{
			pun[1][0] = mag[i][2];
			pun[1][1] = mag[i][3];
		}
		else
		{
			//printf("%d\n", i);
			pun[1][0] = mag[i][0];
			pun[1][1] = mag[i][1];
		}
		if (sorwek(-500, 0, pun[1][0] - pun[0][0], pun[1][1] - pun[0][1], pun[2][0] - pun[0][0], pun[2][1] - pun[0][1]) == 2)
		{
			pun[2][0] = pun[1][0];
			pun[2][1] = pun[1][1];
			nr2 = i;
		}
	}
	nr3 = nr2;
	pun[3][0] = pun[2][0];
	pun[3][1] = pun[2][0];
	pun[0][0] = mag[nr1][2];
	pun[0][1] = mag[nr1][3];
	pun[2][0] = pun[0][0] - 1;
	pun[2][1] = pun[0][1];
	for (int i = 0; i < n; i++)
	{
		if (i == nr1)continue;
		if (to[i] == 1)continue;
		if (sorwek(-502, 0, mag[i][0] - pun[0][0], mag[i][1] - pun[0][1], mag[i][2] - pun[0][0], mag[i][3] - pun[0][1]) == 2)
		{
			pun[1][0] = mag[i][2];
			pun[1][1] = mag[i][3];
		}
		else
		{
			//printf("%d\n", i);
			pun[1][0] = mag[i][0];
			pun[1][1] = mag[i][1];
		}
		if (sorwek(-500, 0, pun[1][0] - pun[0][0], pun[1][1] - pun[0][1], pun[2][0] - pun[0][0], pun[2][1] - pun[0][1]) == 2)
		{
			pun[2][0] = pun[1][0];
			pun[2][1] = pun[1][1];
			nr2 = i;
		}
	}
	if (sorwek(-1, 0, pun[3][0] - mag[nr1][0], pun[3][1] - mag[nr1][1], pun[2][0] - mag[nr1][2], pun[2][1] - mag[nr1][3]) == 2)
	{
		nr2 = nr3;
		pun[2][0] = pun[3][0];
		pun[2][1] = pun[3][1];
		pun[0][0] = mag[nr1][0];
		pun[0][1] = mag[nr1][1];
	}
	else
	{
		pun[0][0] = mag[nr1][2];
		pun[0][1] = mag[nr1][3];
	}
	prost[0].push_back(pun[0][0]);
	prost[1].push_back(pun[0][1]);
	prost[2].push_back(pun[2][0]);
	prost[3].push_back(pun[2][1]);
	kom.push_back(nr1);
	kom.push_back(nr2);



	for (int j = 0; nr2 != nrp; j++)
	{
		nr1 = nr2;
		to[nr1] = 1;
		pun[0][0] = mag[nr1][0];
		pun[0][1] = mag[nr1][1];
		pun[2][0] = pun[0][0];
		pun[2][1] = pun[0][1];
		for (int i = 0; i < n; i++)
		{
			if (to[i] == 1)continue;
			if (sorwek(prost[2][j] - prost[0][j], prost[1][j] - prost[1][j], mag[i][0] - pun[0][0], mag[i][1] - pun[0][1], mag[i][2] - pun[0][0], mag[i][3] - pun[0][1]) == 2)
			{
				pun[1][0] = mag[i][2];
				pun[1][1] = mag[i][3];
			}
			else
			{
				//printf("%d\n", i);
				pun[1][0] = mag[i][0];
				pun[1][1] = mag[i][1];
			}
			if (sorwek(prost[2][j] - prost[0][j], prost[1][j] - prost[1][j], pun[1][0] - pun[0][0], pun[1][1] - pun[0][1], pun[2][0] - pun[0][0], pun[2][1] - pun[0][1]) == 2)
			{
				pun[2][0] = pun[1][0];
				pun[2][1] = pun[1][1];
				nr2 = i;
			}
		}
		nr3 = nr2;
		pun[3][0] = pun[2][0];
		pun[3][1] = pun[2][1];
		pun[0][0] = mag[nr1][2];
		pun[0][1] = mag[nr1][3];
		pun[2][0] = pun[0][0];
		pun[2][1] = pun[0][1];
		for (int i = 0; i < n; i++)
		{
			if (to[i] == 1)continue;
			if (sorwek(prost[2][j] - prost[0][j], prost[1][j] - prost[1][j], mag[i][0] - pun[0][0], mag[i][1] - pun[0][1], mag[i][2] - pun[0][0], mag[i][3] - pun[0][1]) == 2)
			{
				pun[1][0] = mag[i][2];
				pun[1][1] = mag[i][3];
			}
			else
			{
				//printf("%d\n", i);
				pun[1][0] = mag[i][0];
				pun[1][1] = mag[i][1];
			}
			if (sorwek(prost[2][j] - prost[0][j], prost[1][j] - prost[1][j], pun[1][0] - pun[0][0], pun[1][1] - pun[0][1], pun[2][0] - pun[0][0], pun[2][1] - pun[0][1]) == 2)
			{
				pun[2][0] = pun[1][0];
				pun[2][1] = pun[1][1];
				nr2 = i;
			}
		}
		if (sorwek(prost[2][j] - prost[0][j], prost[1][j] - prost[1][j], pun[3][0] - mag[nr1][0], pun[3][1] - mag[nr1][1], pun[2][0] - mag[nr1][2], pun[2][1] - mag[nr1][3]) == 2)
		{
			//printf(".");
			nr2 = nr3;
			pun[2][0] = pun[3][0];
			pun[2][1] = pun[3][1];
			pun[0][0] = mag[nr1][0];
			pun[0][1] = mag[nr1][1];
		}
		else
		{
			pun[0][0] = mag[nr1][2];
			pun[0][1] = mag[nr1][3];
		}
		prost[0].push_back(pun[0][0]);
		prost[1].push_back(pun[0][1]);
		prost[2].push_back(pun[2][0]);
		//printf("%d",pun[2][1]);
		prost[3].push_back(pun[2][1]);
		kom.push_back(nr2);
		if (j > n + 2)
		{
			printf("0.000000000");
			return 0;
		}
	}




	si = prost[0].size();
	for (int j = 1; j < n; j++)
	{
		if (prost[0][j] == prost[2][j - 1] && prost[1][j] == prost[3][j - 1])continue;
		dob1 = polet(prost[0][j - 1], prost[1][j - 1], prost[0][j], prost[1][j], prost[2][j], prost[3][j]);
		dob2 = polet(prost[2][j - 1], prost[3][j - 1], prost[0][j], prost[1][j], prost[2][j], prost[3][j]);
		dob3 = dob1 / (dob1 + dob2);
		dob1 = (prost[2][j - 1] - prost[0][j - 1])*dob3 + prost[0][j - 1];
		dob2 = (prost[3][j - 1] - prost[1][j - 1])*dob3 + prost[1][j - 1];
		prost[2][j - 1] = dob1;
		prost[3][j - 1] = dob2;
		prost[0][j] = dob1;
		prost[1][j] = dob2;
	}
	if (prost[0][0] != prost[2][si - 1] || prost[1][0] != prost[3][si - 1])
	{
		dob1 = polet(prost[0][si - 1], prost[1][si - 1], prost[0][0], prost[1][0], prost[2][0], prost[3][0]);
		dob2 = polet(prost[2][si - 1], prost[3][si - 1], prost[0][0], prost[1][0], prost[2][0], prost[3][0]);
		dob3 = dob1 / (dob1 + dob2);
		dob1 = (prost[2][si - 1] - prost[0][si - 1])*dob3 + prost[0][si - 1];
		dob2 = (prost[3][si - 1] - prost[1][si - 1])*dob3 + prost[1][si - 1];
		prost[2][si - 1] = dob1;
		prost[3][si - 1] = dob2;
		prost[0][0] = dob1;
		prost[1][0] = dob2;
	}
	for (int i = 2; i < si; i++)
	{
		//printf("%Lf %Lf\n", prost[0][i], prost[1][i]);
		wyn += polet(prost[0][0], prost[1][0], prost[0][i - 1], prost[1][i - 1], prost[0][i], prost[1][i]);
	}
	printf("%.10Lf\n", wyn);
	//printf("%Lf",dob);
	/*for (int i = 0; i < prost[0].size(); i++)
	{
	printf("%d %d %d %d %d\n", prost[0][i], prost[1][i], prost[2][i], prost[3][i], kom[i +1]);
	}*/
	//printf("%d %d %d %d %d %d ",nr1, pun[0][0], pun[0][1] , nr2,pun[2][0],pun[2][1]);
	//printf("\n%d %d     %d", pun[0][0], pun[0][1], nr1);
	//system("PAUSE");
}