#include<cstdio>
#include<vector>
#include<algorithm>
using namespace std;
#define NMAX 20001
#define INF 1000000
#define pb push_back
int N,k1,k2;
struct punct
{double x , y;}P[NMAX] ,pol1[4*NMAX] , pol2[4*NMAX];
float A;
double det(punct p1 , punct p2 ,punct p3)
{
return p1.x*p2.y + p2.x*p3.y + p3.x*p1.y - p2.y*p3.x - p3.y*p1.x - p2.x*p1.y;
}
void coef(punct p1 , punct p2 , double &a , double &b , double &c)
{
a = p2.y-p1.y;
b = p1.x-p2.x;
c = p1.y*p2.x-p1.x*p2.y;
}
punct intersect(double a1 , double b1 , double c1 , double a2 , double b2 , double c2)
{
punct p;
p.x = (b1*c2-b2*c1)/(a1*b2-a2*b1);
p.y = (a1*c2-a2*c1)/(b1*a2-b2*a1);
return p;
}
int semn(double a , double b , double c , punct p)
{
if(a*p.x+b*p.y+c > 0)return 0;
return 1;
}
int main()
{
freopen("camera.in" , "r" , stdin );
freopen("camera.out" , "w" , stdout );
scanf("%d" , &N );
for(int i = 1 ; i<= N ; ++i )
scanf("%lf%lf" , &P[i].x , &P[i].y );
P[N+1] = P[1];
for(int i = 1 ; i <= N ; ++i )
A+=det(P[0],P[i],P[i+1]);
if(A < 0)reverse(P+1,P+N+1);
punct p;
p.x = -INF,p.y = -INF;pol1[1] = p;
p.x = INF;pol1[2] = p;
p.y = INF;pol1[3] = p;
p.x =-INF;pol1[4] = p;
pol1[5] = pol1[1];
k1 = 4;
double a,b,c,a1,b1,c1;
for(int i = 1 ; i <= N ; ++i )
{
k2 = 0;
coef(P[i],P[i+1],a,b,c);
for(int j = 1 ; j <= k1 ; ++j )
{
int d1 = semn(a,b,c,pol1[j]) , d2 = semn(a,b,c,pol1[j+1]) ;
coef(pol1[j],pol1[j+1],a1,b1,c1);
if(d1)
{
if(d2) pol2[++k2] = pol1[j+1];
else pol2[++k2] = intersect(a,b,c,a1,b1,c1);
}
else
if(d2){ pol2[++k2] = intersect(a,b,c,a1,b1,c1);
pol2[++k2] = pol1[j+1];}
}
for(int i = 1 ; i<= k2 ; ++i )
pol1[i] = pol2[i];
k1 = k2;
pol1[k1+1] = pol1[1];
}
A = 0;
for(int i = 1 ; i<= k1 ; ++i )
A+=det(P[0],pol1[i],pol1[i+1]);
if(A < 0)A = -A;
A/=2;
printf("%.2f" , A);
return 0;
}