#include <iostream>
#include <iomanip>
#include <cstdlib>
using namespace std;
int main(){int n,m;cin>>n;long double x,y,c=0,d=0,e=0,f=0,g=0,h,nn;
for(m=0;m<n;m++){cin>>x>>y;c+=x;d+=y;g+=x*y;e+=x*x;f+=y*y;}nn=n;
h=f+(((nn*g-c*d)*(nn*g-c*d)*e+nn*(e*d-c*g)*(e*d-c*g)+2.L*(nn*g-c*d)*(e*d-c*g)*c)
/(nn*e-c*c)-(2.L*(nn*g-c*d)*g+2.L*(e*d-c*g)*d))/(nn*e-c*c);cout<<setprecision(20)<<h;return 0;}