#include <bits/stdc++.h>
using namespace std;
const int B = 70; const double pi = acos(-1);
int n; double ans = 0,s = 0,x[500010],y[500010],tmp[500010];
int main() {
	cin.tie(0)->sync_with_stdio(false);
	cin >> n; for(int i = 1; i <= n; i++) cin >> x[i] >> y[i]; x[0] = 1,y[0] = 0;
	for(int g = 0; g < B; g++) {
		for(int i = 1; i <= n; i++) tmp[i] = x[i];
		sort(tmp+1,tmp+1+n); s += abs(x[0]);
		for(int i = 1; i <= n; i++) ans += (2*i-n-2)*tmp[i];
		for(int i = 0; i <= n; i++) {
			double xx = x[i]*cos(2*pi/B)-y[i]*sin(2*pi/B);
			double yy = x[i]*sin(2*pi/B)+y[i]*cos(2*pi/B);
			x[i] = xx,y[i] = yy;
		}
	}
	cout << fixed << setprecision(10) << ans/s;
	return 0;
}