#include<bits/stdc++.h>
#define LL long long
#define LLL __int128
#define uint unsigned
#define ldb long double
#define uLL unsigned long long
using namespace std;
const int N=5e5+5,B=35;
const ldb pi=acosl(-1);
int n,id[N];ldb s,ans,val[N];pair<int,int>A[N];
signed main(){
	cin.tie(0)->sync_with_stdio(0);
	cin>>n;
	for(int i=0;i<n;++i)cin>>A[i].first>>A[i].second;
	for(int k=0;k<B;++k){
		const ldb x=cosl(pi*k/B),y=-sinl(pi*k/B);
		for(int i=0;i<n;++i)val[i]=A[i].first*x+A[i].second*y,id[i]=i;
		sort(id,id+n,[&](const int&x,const int&y){return val[x]<val[y];});
		s=0;for(int i=0;i<n;++i)ans+=val[id[i]]*i-s,s+=val[id[i]];
		s=0;for(int i=n;i--;)ans+=s-val[id[i]]*(n-i-1),s+=val[id[i]];
	}
	cout<<fixed<<setprecision(10)<<ans*pi/B/4<<'\n';
	return 0;
}
/*
*/