#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <functional>
#include <iostream>
#include <limits>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

using namespace std;

using Int = long long;

template <class T1, class T2> ostream &operator<<(ostream &os, const pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << endl; }
template <class T> bool chmin(T &t, const T &f) { if (t > f) { t = f; return true; } return false; }
template <class T> bool chmax(T &t, const T &f) { if (t < f) { t = f; return true; } return false; }
#define COLOR(s) ("\x1b[" s "m")


using Double = long double;
const Double EPS = 1e-10L;
const Double INF = 1e+10L;
const Double PI = acos(-1.0L);
inline int sig(Double r) { return (r < -EPS) ? -1 : (r > +EPS) ? +1 : 0; }
inline Double sq(Double r) { return r * r; }

struct Pt {
  Double x, y;
  Pt() {}
  Pt(Double x_, Double y_) : x(x_), y(y_) {}
  Pt operator+(const Pt &a) const { return Pt(x + a.x, y + a.y); }
  Pt operator-(const Pt &a) const { return Pt(x - a.x, y - a.y); }
  Pt operator*(const Pt &a) const { return Pt(x * a.x - y * a.y, x * a.y + y * a.x); }
  Pt operator/(const Pt &a) const { const Double d2 = a.abs2(); return Pt((x * a.x + y * a.y) / d2, (y * a.x - x * a.y) / d2); }
  Pt operator+() const { return Pt(+x, +y); }
  Pt operator-() const { return Pt(-x, -y); }
  Pt operator*(const Double &k) const { return Pt(x * k, y * k); }
  Pt operator/(const Double &k) const { return Pt(x / k, y / k); }
  friend Pt operator*(const Double &k, const Pt &a) { return Pt(k * a.x, k * a.y); }
  Pt &operator+=(const Pt &a) { x += a.x; y += a.y; return *this; }
  Pt &operator-=(const Pt &a) { x -= a.x; y -= a.y; return *this; }
  Pt &operator*=(const Pt &a) { return *this = *this * a; }
  Pt &operator/=(const Pt &a) { return *this = *this / a; }
  Pt &operator*=(const Double &k) { x *= k; y *= k; return *this; }
  Pt &operator/=(const Double &k) { x /= k; y /= k; return *this; }
  Double abs() const { return sqrt(x * x + y * y); }
  Double abs2() const { return x * x + y * y; }
  Double arg() const { return atan2(y, x); }
  Double dot(const Pt &a) const { return x * a.x + y * a.y; }
  Double det(const Pt &a) const { return x * a.y - y * a.x; }
  friend ostream &operator<<(ostream &os, const Pt &a) { os << "(" << a.x << ", " << a.y << ")"; return os; }
  bool operator<(const Pt &a) const { return (x != a.x) ? (x < a.x) : (y < a.y); }
};
inline Double tri(const Pt &a, const Pt &b, const Pt &c) { return (b - a).det(c - a); }


/*
  S[i] = det(d, P[i+1] - P[i])
       = det(d, P[i+1]) - det(d, P[i])
  cool <=> \exists i, det(d, P[i]) and det(d, P[i+1]) are min and max
*/

int N;
vector<Pt> P;

int main() {
  for (; ~scanf("%d", &N); ) {
    P.resize(N);
    for (int i = 0; i < N; ++i) {
      int x, y;
      scanf("%d%d", &x, &y);
      P[i] = Pt(x, y);
    }
    
    {
      Double area = 0.0;
      for (int i = 0; i < N; ++i) {
        area += P[i].det(P[(i + 1) % N]);
      }
      if (area < 0) {
        reverse(P.begin(), P.end());
      }
    }
    
    vector<Double> as(N);
    for (int i = 0; i < N; ++i) {
      as[i] = ((P[(i - 1 + N) % N] - P[i]) / (P[(i + 1) % N] - P[i])).arg();
    }
    Double ans = 0.0;
    for (int i = 0; i < N; ++i) {
      ans += max(PI - as[i] - as[(i + 1) % N], 0.0L);
    }
    ans /= PI;
    printf("%.20Lf\n", ans);
  }
  return 0;
}