#include<bits/stdc++.h>
using namespace std;
const int N=200010;
const double pi=acos(-1);
double a[N];
struct point{
	int x,y;
	double len(){
		return sqrt(x*x+y*y);
	}
}p[N];
point operator-(point a,point b){
	return {a.x-b.x,a.y-b.y};
}
double operator*(point a,point b){
	return a.x*b.x+a.y*b.y;
}
int main(){
	int n;
	double ans=0;
	scanf("%d",&n);
	for(int i=1;i<=n;i++){
		scanf("%d%d",&p[i].x,&p[i].y);
	}
	p[0]=p[n];
	p[n+1]=p[1];
	for(int i=1;i<=n;i++){
		a[i]=acos((p[i-1]-p[i])*(p[i+1]-p[i])/(p[i-1]-p[i]).len()/(p[i+1]-p[i]).len());
	}
	a[0]=a[n];
	a[n+1]=a[1];
	for(int i=1;i<=n;i++){
		if(a[i]+a[i+1]<pi){
			ans+=(pi-a[i]-a[i+1])/pi;
		}
	}
	printf("%.15lf",ans);
}