#include <bits/stdc++.h>
#define x first
#define y second
#define point pair<double,double>
using namespace std;
ifstream f("camera.in");
ofstream g("camera.out");
int n;
double area;
double sumx,sumy;
vector<point> p,r,a;

bool cmp(point po1,point po2)
{
    return atan2(po1.x - sumx / n,po1.y - sumy / n) > atan2(po2.x - sumx / n,po2.y - sumy / n);
}

void Read()
{
    int x,y;
    f>>n;
    for(int i=1;i<=n;++i)
    {
        f>>x>>y;
        sumx += x;
        sumy += y;
        p.push_back(make_pair(x,y));
    }

    r = p;
}

point intersection(point po1,point po2,point po3,point po4)
{
    double x1 = po1.y - po2.y;
    double y1 = po2.x - po1.x;
    double c1 = po1.x * po2.y - po2.x * po1.y;
    double x2 = po3.y - po4.y;
    double y2 = po4.x - po3.x;
    double c2 = po3.x * po4.y - po4.x * po3.y;
    double x = (y1 * c2 - y2 * c1) / (x1 * y2 - x2 * y1);
    double y = (c2 * x1 - c1 * x2) / (y1 * x2 - y2 * x1);

    return {x , y};
}

int cross_product(point po1,point po2,point po3)
{
    return (po2.y - po3.y) * (po1.x - po3.x) - (po1.y - po3.y) * (po2.x - po3.x);
}

void Prepare()
{
    p.push_back(p[0]);
    p.push_back(p[1]);
}

void Solve()
{
    for(int i = 5;i < p.size() - 1;++i)
    {
        a.clear();

        r.push_back(r[0]);

        for(int j = 0;j < r.size() - 1;++j)
        {
            point curr = r[j];
            point next = r[j + 1];

            if(cross_product(p[i],p[i + 1],curr) > 0)
            {
                if(cross_product(p[i],p[i + 1],next) > 0)
                    a.push_back(next);
                else
                    a.push_back(intersection(p[i],p[i + 1],curr,next));
            }
            else
            {
                if(cross_product(p[i],p[i + 1],next) >= 0)
                {
                    a.push_back(intersection(p[i],p[i + 1],curr,next));
                    a.push_back(next);
                }
            }
        }

        r.clear();
        r.assign(a.begin(),a.end());
    }
}

void calculate_area()
{
    r.push_back(r[0]);
    for(int i = 0;i < r.size() - 1;++i)
        area += r[i].x * r[i + 1].y - r[i + 1].x * r[i].y;
    if(area < 0)
        area = -area;
    area /= 2.0;
}

void Print()
{
    g<<setprecision(2)<<fixed;
    g<<area;
    g.close();
}
int main()
{
    Read();
    if( n > 4)
    {
        Prepare();
        Solve();
    }
    calculate_area();
    Print();
    return 0;
}