#include <bits/stdc++.h>
using namespace std;
#define PI 2*acos(0.0)
int main()
{
double r ,n,a,ans;
while(scanf("%lf %lf",&r,&n)==2)
{
a=(r*r*sin(2*PI/n))/2;
ans=n*a;
printf("%.3lf\n",ans);
}
return 0;
}
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