#include<bits/stdc++.h>
#define ll long long
#define Il inline
#define mem(u,v) memset(u,v,sizeof(u))
#define rep(i,a,b) for(ll i=(a),KKK##i=(b);i<=KKK##i;i++)
#define drep(i,a,b) for(ll i=(a),KKK##i=(b);i>=KKK##i;i--)
#define go(u) for(ll i=head[u],v=e[i].to;i;i=e[i].nxt,v=e[i].to)
#define writesp(x) write(x),putchar(' ')
#define writeln(x) write(x),puts("")
using namespace std;
Il ll read(){ll sum=0,f=0;char ch=getchar();for(;!isdigit(ch);ch=getchar())f|=(ch=='-');for(;isdigit(ch);ch=getchar())sum=((sum<<1)+(sum<<3)+(ch^48));return f?-sum:sum;}
void write(const ll x){if(x<0){putchar('-');write(-x);return;}if(x>9)write(x/10);putchar(x%10+'0');}
char getc(){char c=getchar();while(!isalpha(c))c=getchar();return c;}
#define N 550000
#define E(x) ((x)*(x))
#define Pi acos(-1)
ll n;double x[N],y[N],X[N],ans;
int main(){
	n=read();rep(i,1,n)x[i]=read(),y[i]=read();
	if(n<=2000){
		rep(i,1,n)rep(j,i+1,n)ans+=sqrt((E(x[i]-x[j])+E(y[i]-y[j])));
		printf("%.10lf",ans);
		return 0;
	}
	double dx=Pi*2/200;
	rep(_,0,199){
		double a=(1.0*_+0.5)*dx,s=sin(a),c=cos(a);
		rep(i,1,n)X[i]=x[i]*c-y[i]*s;
		sort(X+1,X+n+1);
		rep(i,1,n)ans+=X[i]*(i-1-(n-i));
	}
	printf("%.10lf",ans/4);
}