#include <bits/stdc++.h>

#define long long long int
#define DEBUG
using namespace std;

// @author: pashka

double ang(pair<double, double> a, pair<double, double> b) {
    double dx = b.first - a.first;
    double dy = b.second - a.second;
    return atan2(dy, dx);
}

int main() {
    ios::sync_with_stdio(false);

    int n;
    cin >> n;
    vector<pair<double, double>> p(n);
    for (int i = 0; i < n; i++) cin >> p[i].first >> p[i].second;
    double res = 0;
    for (int i = 0; i < n; i++) {
        double a1 = ang(p[i], p[(i + 1) % n]);
        double a2 = ang(p[(i + 2) % n], p[(i + 3) % n]);
        if (a2 < a1) a2 += M_PI * 2;
        double da = a2 - a1;
        res += max(da - M_PI, 0.0);
    }
    cout << setprecision(20) << res / M_PI << "\n";

    return 0;
}