HDU 3201 Build a Fence

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;

const double PI=3.1415926;

int main()
{
double L;
while(~scanf("%lf",&L)){
if(!L) break;
printf("%.2lf\n",(L*L)/(2*PI));
}
return 0;
}