#include <bits/stdc++.h>

using namespace std;

const int N = 1e5 + 5, B = 55;
const double PI = acos(-1.0);

int x[N], y[N];
double res[N];
pair<double, int> tq[N];

signed main() {
    int n; scanf("%d", &n);
    for (int i = 1; i <= n; ++i) scanf("%d%d", &x[i], &y[i]);
    for (int i = 0; i < B; ++i) {
        double s1 = cos(2 * PI * i / B), s2 = sin(2 * PI * i / B), now = 0;
        for (int j = 1; j <= n; ++j) tq[j] = make_pair(s1 * x[j] - s2 * y[j], j);
        sort(tq + 1, tq + n + 1);
        for (int j = 1; j <= n; ++j) res[tq[j].second] += j * tq[j].first - (now += tq[j].first);
        now = 0;
        for (int j = n; j; --j) res[tq[j].second] += (now += tq[j].first) - (n - j + 1) * tq[j].first;
    }
    printf("%.6lf\n", accumulate(res + 1, res + n + 1, (double)0) / B * PI / 4.0);
    return 0;
}