#include<bits/stdc++.h>
#define rep(i, n) for(int i = 0; i < (n); ++i)
using namespace std;
typedef long long ll;
typedef vector<int> vi;
typedef pair<int, int> pii;
const int Mod = 998244353;
inline void uadd(int &a, const int &b){ a += b - Mod; a += (a>>31) & Mod; }
inline int add(int a, const int &b){ a += b - Mod; a += (a>>31) & Mod; return a; }
inline void usub(int &a, const int &b){ a -= b; a += (a>>31) & Mod; }
inline int sub(int a, const int &b){ a -= b, a += (a>>31) & Mod; return a; }
inline void umul(int &a, const int &b){ a = (int)(1ll * a * b % Mod); }
inline int mul(const int &a, const int &b){ return (int)(1ll * a * b % Mod); }
int qpow(int b, ll p){ int ret = 1; while(p){ if(p & 1) umul(ret, b); umul(b, b), p >>= 1; } return ret; }
const int fN = 10010;
int fact[fN], invfact[fN], inv[fN];
void initfact(int n){
	fact[0] = 1; for(int i = 1; i <= n; ++i) fact[i] = mul(fact[i - 1], i);
	invfact[n] = qpow(fact[n], Mod - 2); for(int i = n; i > 0; --i) invfact[i - 1] = mul(invfact[i], i);
	for(int i = 1; i <= n; ++i) inv[i] = mul(invfact[i], fact[i - 1]);
}
inline int binom(int n, int m){ return mul(fact[n], mul(invfact[m], invfact[n - m])); }

const int inf = 0x3f3f3f3f;
const ll INF = 0x3f3f3f3f3f3f3f3fll;
template<typename T> inline void chmax(T &_a, const T &_b){ (_b>_a) ? (_a=_b) : _a; }
template<typename T> inline void chmin(T &_a, const T &_b){ (_b<_a) ? (_a=_b) : _a; }

const double eps = 1e-8;
const double pi = acos(-1);
inline int sign(double x){ return (x > eps ? +1 : (x < -eps ? -1 : 0)); }
struct vec{
	int x, y;
	vec(int _x = 0, int _y = 0){ x = _x, y = _y; }
};
double getang(vec v){ return atan2(v.y, v.x); }
inline bool operator <(vec lh, vec rh){ return ((lh.x != rh.x) ? (lh.x < rh.x) : (lh.y < rh.y)); } // 比大小，先比 x 后比 y
inline double len(vec v){ return sqrt(1.*v.x*v.x + 1.*v.y*v.y); } // 模长
inline vec operator +(vec lh, vec rh){ return vec(lh.x + rh.x, lh.y + rh.y); } // 向量加
inline vec operator -(vec lh, vec rh){ return vec(lh.x - rh.x, lh.y - rh.y); } // 向量减
inline ll dot(vec lh, vec rh){ return 1ll * lh.x * rh.x + 1ll * lh.y * rh.y; } // 向量点乘
inline ll cross(vec lh, vec rh){ return 1ll * lh.x * rh.y - 1ll * lh.y * rh.x; } // 向量叉乘

int n;
vec v[200200];

int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);

	cin >> n;
	rep(i, n) cin >> v[i].x >> v[i].y;
	if(cross(v[1] - v[0], v[2] - v[1]) < 0) reverse(v, v + n);
	double ans = 0;
	rep(i, n) if(cross(v[(i + 1) % n] - v[i], v[(i + 3) % n] - v[(i + 2) % n]) < 0){
		double ang = getang(v[(i + 2) % n] - v[(i + 3) % n]) - getang(v[(i + 1) % n] - v[i]);
		while(ang < 0) ang += 2. * pi;
		while(ang > 2. * pi) ang -= 2. * pi;
		ans += ang / pi;
	}
	cout << fixed << setprecision(12) << ans << "\n";

	return 0;
}