#include<cstdio>
#include<cmath> 
#define db double
using namespace std;
const db pi=acos(-1.0);
const int N=1e6+100;
int n;
struct comp
{
	db x,y;
}p[N+10];
comp operator -(comp x,comp y)
{
	return (comp){x.x-y.x,x.y-y.y}; 
}
db lent(comp x){return sqrt(x.x*x.x+x.y*x.y);}
db getangle(comp x,comp y)
{
	return acos(abs(x.x*y.x+x.y*y.y)/lent(x)/lent(y));
}
db across(comp x,comp y)
{
	return x.x*y.y-x.y*y.x; 
}
int id(int x)
{
	if(x<=0) x+=n;
	if(x>n) x-=n;
	return x;
}
int main()
{
//	freopen("ll.in","r",stdin);
	scanf("%d",&n);
	for(int i=1;i<=n;i++)
		scanf("%lf %lf",&p[i].x,&p[i].y);
//	printf("%lf\n",getangle(p[2],p[3]));
	db ans=0;
	for(int i=1;i<=n;i++)
	{
		comp x=p[i]-p[id(i-1)],y=p[id(i+1)]-p[id(i+2)];
		if(across(x,y)>0){
//			printf("%d %d %lf\n",i,i+1,getangle(x,y));
//			printf("%lf %lf %lf %lf\n",x.x,x.y,y.x,y.y);
			ans+=getangle(x,y);
		}
	}
	printf("%lf\n",ans/pi);
	return 0;
}