#include <bits/stdc++.h>
#define ll long long
using namespace std;

const int N = 5e5 + 5;
const long double pi = acos((long double) -1);
ll n, x[N], y[N];
long double ans;

int main() {
    scanf ("%lld", &n);
    vector<pair<int, int> >a(n);
    for (auto &[x, y] : a) scanf ("%d%d", &x, &y);
    for (int i = 0; i < 180; ++i) {
        long double t = pi / 180 * i, c = cos(t), s = sin(t);
        vector<long double> p;
        for (auto[x, y] : a) p.emplace_back(x * c - y * s);
        sort(begin(p), end(p));
        for (auto j : p) ans += j * (i * 2 - n + 1);
    }
    printf ("%.20Lf\n", ans * pi / 200);
    return 0;
}