timus1084

#include <iostream>
#include <cstdio>
#include <cmath>
using namespace std;
double pi=3.14159265359;
int main()
{
    double l,r;
    double s;
    cin>>l>>r;
    if(r<=l/2.)
        s=pi*r*r;
    else
    if(r<=sqrt(2.)*l/2. && r>l/2.)
    {
        double a=asin(l/(2.*r));
        double f=pi-2*a;
        double sect=r*r/2.*(f-sin(f));
        s=pi*r*r-4*sect;
    }
    else
        s=l*l;
    printf("%0.3f",s);
    return 0;
}