#include <bits/stdc++.h>
using namespace std;
ifstream f("aria.in");
ofstream g("aria.out");
struct punct
{
    long double X,Y;
    punct()
    {
        X=Y=0.0;
    }
    punct(long double x,long double y)
    {
        X=x;Y=y;
    }
};
int n;
long double xd,yd,xs,ys,xi,yi,sol;
int main()
{
    f>>n;
    f>>xi>>yi;
    xs=xi;ys=yi;
    for(int i=2;i<=n;i++)
        f>>xd>>yd;

    g<<sol;

    return 0;
}