#include<bits/stdc++.h>

using namespace std;

using db = double;

const db eps = 1e-9;
int sign(db a){ return a < -eps ? -1 : a > eps; }
int cmp(db a, db b) { return sign(a - b); }

struct P {
	db x, y;

	P operator+(P p) { return {x + p.x, y + p.y}; }
	P operator-(P p) { return {x - p.x, y - p.y}; }

	bool operator<(P p) const {
		int c = cmp(x, p.x);
		if(c) return c == -1;
		return cmp(y, p.y) == -1;
	}
	bool operator==(P p) const {
		return cmp(x, p.x) == 0 && cmp(y, p.y) == 0;
	}

	db dot(P p){ return x * p.x + y * p.y; }
	db det(P p){ return x * p.y - y * p.x; }

};

db rad(P p1, P p2){
	return atan2(p1.det(p2), p1.dot(p2));
}

#define cross(p1, p2, p3) ((p2.x - p1.x) * (p3.y - p1.y) - (p3.x - p1.x) * (p2.y - p1.y))
#define crossOp(p1, p2, p3) sign(cross(p1, p2, p3))

signed main(){
	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	int n;
	cin >> n;

	vector<P> p(n);
	for(int i = 0; i < n; i++)
		cin >> p[i].x >> p[i].y;

	db ans = 0;
	for(int i = 0; i < n; i++){
		P a = p[(i + 1) % n] - p[i];
		P b = p[(i + n - 2) % n] - p[(i + n - 1) % n];

		// cerr << fixed << setprecision(20) << rad(a, b) << "\n";
		// cerr << a.x << " " << a.y << "|" << b.x << " " << b.y << "\n";

		ans += max(0.0, -rad(a, b));
	}

	// for(auto i : h)
	// 	cerr << i.x << " " << i.y << "\n";

	ans = ans / acos(-1.0); 

	cout << fixed << setprecision(20) << ans << "\n";
}
/*
4
0 0
0 3
1 2
1 1
*/