#include <bits/stdc++.h>
using namespace std;
template <typename T>inline void read(T &x)
{
    x=0;char c=getchar();bool f=0;
    for(;c<'0'||c>'9';c=getchar())f|=(c=='-');
    for(;c>='0'&&c<='9';c=getchar())x=(x<<1)+(x<<3)+(c-'0');
    x=(f?-x:x);
}
const int N = 2e5+7;
int n;
typedef double db;
const db pi =acos(-1);
struct node
{
    double x,y;
}p[N],q[N];
node operator -(node a,node b)
{
    return (node){a.x-b.x,a.y-b.y};
}
double arc[N];
double ang(node v)
{
    return atan2(v.y,v.x);
}
double mod(double t)
{
    while(t<0)t+=2.0*pi;
    while(t>2.0*pi)t-=2.0*pi;
    return t;
}
int main()
{
    cin>>n;
    for(int i=0;i<n;i++)
    {
        scanf("%lf %lf",&q[i].x,&q[i].y);
    }
    for(int i=0;i<n;i++)p[i]=q[(i+1)%n]-q[i];
    for(int i=0;i<n;i++)
    arc[i]=mod(pi+ang(p[(i+1)%n])-ang(p[i]));
    db res=0;
    for(int i=0;i<n;i++)
    {
        res+=max(0.0,pi-arc[i]-arc[(i+1)%n]);
    }
    res/=pi;
    printf("%.10lf",res);
	return 0;
}