#include <bits/stdc++.h>
#define For(i,a,b) for(int i=a;i<=b;i++)
#define Rev(i,a,b) for(int i=a;i>=b;i--)
#define Fin(file) freopen(file,"r",stdin)
#define Fout(file) freopen(file,"w",stdout)
using namespace std;
// #define cout Cout
const int N=5e5+5; typedef long long ll; const double PI=acos(-1.0);
int read()
{
    bool neg=false;
    char Charlie;
    while((Charlie=getchar())<'0'||Charlie>'9'){
        if(Charlie=='-') neg=true;
    }
    int Vinnie=Charlie-'0';
    while((Charlie=getchar())>='0'&&Charlie<='9') Vinnie=(Vinnie<<3)+(Vinnie<<1)+Charlie-'0';
    return neg?-Vinnie:Vinnie;
}
int n,px[N],py[N]; double tx[N];
signed main(){
    n=read(); For(i,1,n) { px[i]=read(); py[i]=read(); }
    if(n<=4000){
        double ans=0.0; For(i,1,n) For(j,i+1,n) ans+=sqrt((px[i]-px[j])*(px[i]-px[j])+(py[i]-py[j])*(py[i]-py[j]));
        cout<<setprecision(20)<<fixed<<ans<<'\n'; return 0;
    }
    int T=100; double dx=2*PI/T,ans=0.0;
    For(i,0,T-1){
        double th=(i+0.5)*dx,costh=cos(th),sinth=sin(th);
        For(j,1,n) tx[j]=px[j]*costh-py[j]*sinth;
        sort(tx+1,tx+1+n); For(j,1,n) ans+=((j-1)-(n-j))*tx[j];
    }
    cout<<setprecision(20)<<fixed<<ans*dx/4<<'\n';
    cerr<<"Time = "<<clock()<<" ms"<<endl;
    return 0;
}

// START TYPING IF YOU DON'T KNOW WHAT TO DO