#include <bits/stdc++.h>
using namespace std;
#define int long long
#define N 200005
struct Vec
{
	int x,y;
	Vec(int a=0,int b=0) {x=a,y=b;}
	double norm() {return sqrt(x*x+y*y);}
};
Vec operator + (Vec x,Vec y) {return Vec(x.x+y.x,x.y+y.y);}
Vec operator - (Vec x,Vec y) {return Vec(x.x-y.x,x.y-y.y);}
int cross(Vec x,Vec y) {return 1LL*x.x*y.y-1LL*x.y*y.x;}
int cdot(Vec x,Vec y) {return 1LL*x.x*y.x+1LL*x.y*y.y;}
int sgn(int x)
{
	if(x<0) return -1;
	else if(x==0) return 0;
	else return 1;
}
int ccw(Vec x,Vec y,Vec z) {return cross(y-x,z-x);}
int n;
Vec a[N];
const double pi=acos(-1);
signed main() {
#ifdef xay5421
	freopen("b.in","r",stdin);
#else
	ios::sync_with_stdio(0),cin.tie(0);
#endif
	cin>>n;
	for(int i=0;i<n;i++) cin>>a[i].x>>a[i].y;
	if(ccw(a[0],a[1],a[2])==-1) reverse(a,a+n);
	double ans=0;
	for(int i=0;i<n;i++)
	{
		if(sgn(cross(a[(i-1+n)%n]-a[i],a[(i+2)%n]-a[(i+1)%n]))==1)
		{
			double w=cross(a[(i-1+n)%n]-a[i],a[(i+2)%n]-a[(i+1)%n]);
			w/=(a[(i-1+n)%n]-a[i]).norm();
			w/=(a[(i+2)%n]-a[(i+1)%n]).norm();
			ans+=asin(w);
		}
	}
	printf("%.10lf\n",ans/pi);
	return 0;
}