#include <bits/stdc++.h>

using namespace std;
typedef long double ld;
ld cross(const pair<int, int>& p1, const pair<int, int>& p2) {
    return p1.first * p2.second - p1.second * p2.first;
}

ld dot(const pair<int, int>& p1, const pair<int, int>& p2) {
    return p1.first * p2.first + p1.second * p2.second;
}

pair<int, int> sub(const pair<int, int>& p1, const pair<int, int>& p2) {
    return make_pair(p1.first - p2.first, p1.second - p2.second);
}

int main() {
    int n;
    cin >> n;

    vector<pair<int, int>> pi(n);

    for (int i = 0; i < n; ++i) {
        cin >> pi[i].first >> pi[i].second;
    }

    if (cross(sub(pi[1], pi[0]), sub(pi[2], pi[0])) < 0) {
        reverse(pi.begin(), pi.end());
    }

    pi.insert(pi.end(), pi.begin(), pi.end());

    vector<ld> poly;

    for (int i = 1; i <= n; ++i) {
        auto x = sub(pi[i + 1], pi[i]);
        auto y = sub(pi[i - 1], pi[i]);
        poly.push_back(acos(dot(x, y) / sqrt(dot(x, x) * dot(y, y))));
    }

    poly.insert(poly.end(), poly.begin(), poly.end());

    ld ans = 0.0;

    for (int i = 0; i < n; ++i) {
        ans += max(ld(0.0), ld(M_PI) - ld(poly[i] + poly[i + 1])) * ld(2);
    }

    cout << fixed << setprecision(12) << ans / ld(M_PI) / ld(2.0) << endl;

    return 0;
}