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

const int MN = 200005;
const double PI = atan(1) * 4;

int n;
pair<int, int> a[MN], vec[MN];
#define x first
#define y second

double mag(pair<int, int> vec) {
    return sqrt(vec.x * vec.x + vec.y * vec.y);
}

double dot(pair<int, int> v1, pair<int, int> v2) {
    return v1.x * v2.x + v1.y * v2.y;
}

double get_angle(int i) {
    double prod = dot(vec[i], vec[(i+1)%n]) / (mag(vec[i]) * mag(vec[(i+1)%n]));
    return acos(-prod);
}

int main() {
    cin.tie(0), cin.sync_with_stdio(0);
    cin >> n;
    for (int i = 0; i < n; i++) cin >> a[i].x >> a[i].y;
    for (int i = 0; i < n; i++) {
        vec[i].x = a[(i+1)%n].x - a[i].x;
        vec[i].y = a[(i+1)%n].y - a[i].y;
    }
    double ans = 0;
    for (int i = 0; i < n; i++) {
        double sum = get_angle(i) + get_angle((i + 1) % n);
        if (sum > PI) continue;
        ans += PI - sum;
    }
    printf("%.9f\n", ans / PI);
}