#include <bits/stdc++.h>

using namespace std;

typedef long long ll;

const int MAX_N = 200000 + 5;
const double Pi = acos(-1);

int N;
double x[MAX_N], y[MAX_N];

inline ll cross(int x1, int y1, int x2, int y2) {
    return 1ll * x1 * y2 - 1ll * y1 * x2;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0); cout.tie(0);
    
    cin >> N;
    for (int i = 1; i <= N; i ++) {
        cin >> x[i] >> y[i];
    }
    if (cross(x[2] - x[1], y[2] - y[1], x[3] - x[2], y[3] - y[2]) > 0) {
        reverse(x + 1, x + N + 1);
        reverse(y + 1, y + N + 1);
    }else {
        assert(false);
    }
    double ans = 0;
    for (int i = 1; i <= N; i ++) {
        int pre = i > 1 ? i - 1 : N;
        int j = i < N ? i + 1 : 1;
        int suf = j < N ? j + 1 : 1;
        int dxl = x[i] - x[pre], dyl = y[i] - y[pre];
        int dxr = x[j] - x[suf], dyr = y[j] - y[suf]; 
        if (cross(dxl, dyl, dxr, dyr) < 0) {
            double angl = atan2(dyl, dxl);
            double angr = atan2(dyr, dxr);
            if (angl < angr) angl += Pi * 2;
            ans += (angl - angr) / Pi;
        }
    }
    cout << fixed << setprecision(12) << ans << '\n';
    
    return 0;
}