import math
n, r = map(int, input().split())
d = math.pi - (math.pi/n) - (math.pi/(2*n))
a = r*math.sin(math.pi/n)/math.sin(d)
print(n*a*r*math.sin(math.pi/(2*n)))#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<string>
#include<algorithm>
int n;
double r;
int main(){
scanf("%d%lf",&n,&r);
double A,B,C,a,b,c,s=0;
a=r;B=acos(-1)/(2*n);C=acos(-1)/n;
A=acos(-1)-B-C;
b=a*sin(B)/sin(A);
s=0.5*a*b*sin(C);
s=2*n*s;
printf("%.12f",s);
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