#include <fstream>
#include <algorithm>
#include <string.h>

#define NMax 2010
#define INF 1000000
#define eps 0.0000001

using namespace std;

ifstream f("camera.in");
ofstream g("camera.out");

struct Point {
	double x;
	double y;

	Point() {};
	Point(double _x, double _y) {
		x = _x;
		y = _y;
	}
	bool operator==(Point p1) {
		if (this->x == p1.x && this->y == p1.y)
			return true;
		return false;
	}
} polyg[NMax], crt[NMax], nex[NMax];

int n, nP, newNP;

double mabs(double d1)
{
	if (d1 < 0)
		return -d1;
	return d1;
}

double det(Point p1, Point p2, Point p3)
{
	return p1.x*p2.y + p2.x*p3.y + p3.x*p1.y - p3.x*p2.y - p1.x*p3.y - p2.x*p1.y;
}

double tri_area(Point p1, Point p2)
{
	return p1.x*p2.y - p2.x*p1.y;
}

Point get_intersection_coords(Point p1, Point p2, Point p3, Point p4)
{
	double a1 = p2.y - p1.y;
	double b1 = p1.x - p2.x;
	double c1 = p1.y*p2.x - p1.x*p2.y;

	double a2 = p4.y - p3.y;
	double b2 = p3.x - p4.x;
	double c2 = p3.y*p4.x - p3.x*p4.y;

	Point answ;
	answ.x = (b1*c2 - b2*c1) / (a1*b2 - a2*b1);
	answ.y = (a2*c1 - a1*c2) / (a1*b2 - a2*b1);

	return answ;
}

double dist(Point p1, Point p2)
{
	return (p1.x - p2.x)*(p1.x - p2.x) + (p1.y - p2.y)*(p1.y - p2.y);
}

bool equal_double(double d1, double d2)
{
	if (mabs(d1 - d1) <= eps)
		return true;
	return false;
}

int main()
{
	f >> n;

	Point leftCorner(INF, INF), rightCorner(0, 0), lowest;
	for (int i = 1; i <= n; i++) {
		f >> polyg[i].x >> polyg[i].y;

		if (leftCorner.x > polyg[i].x)
			leftCorner.x = polyg[i].x;
		if (leftCorner.y > polyg[i].y)
			leftCorner.y = polyg[i].y;
		if (rightCorner.x < polyg[i].x)
			rightCorner.x = polyg[i].x;
		if (rightCorner.y < polyg[i].y)
			rightCorner.y = polyg[i].y;
	}
	crt[++nP] = Point(leftCorner.x, leftCorner.y);
	crt[++nP] = Point(rightCorner.x, leftCorner.y);
	crt[++nP] = Point(rightCorner.x, rightCorner.y);
	crt[++nP] = Point(leftCorner.x, rightCorner.y);
	crt[nP + 1] = crt[1];

	polyg[n + 1] = polyg[1];
	double area = 0;
	for (int i = 1; i <= n; i++)
		area += tri_area(polyg[i], polyg[i + 1]);

	if (area < 0)
		for (int i = 1; i <= n / 2; i++)
			swap(polyg[i], polyg[n - i + 1]);
	polyg[n + 1] = polyg[n];

	for (int i = 1; i <= n; i++) { //pol edges
		Point p1 = polyg[i];
		Point p2 = polyg[i + 1];
		for (int j = 1; j <= nP; j++) { //answ edg
			Point p3 = crt[j];
			Point p4 = crt[j + 1];

			if (det(p1, p2, p3) * det(p1, p2, p4) < 0) {
				Point intersection = get_intersection_coords(p1, p2, p3, p4);

				if (det(p1, p2, p4) > 0) {
					nex[++newNP] = intersection;
					nex[++newNP] = p4;
				}
				else
					nex[++newNP] = intersection;
			}
			else
				if (det(p1, p2, p4) >= 0)
					nex[++newNP] = p4;
		}

		nP = newNP;
		newNP = 0;
		swap(crt, nex);
		crt[nP + 1] = crt[1];
		memset(nex, 0, sizeof(nex));
	}

	double answArea = 0;
	for (int i = 1; i <= nP; i++)
		answArea += tri_area(crt[i], crt[i + 1]);

	g << 1.0 * answArea / 2;

	return 0;
}