#include <iostream>
#include <iomanip>
#include <cmath>

using namespace std;

int main()
{
    long double x,y;
    cout <<setprecision(3)<<fixed<<showpoint;
    const long double pi=3.1416;
    cin >>x>>y;
    if(x/2<y)
    {
        if(sqrt(2.0)*x<=y) cout <<x*x<<endl;
        else
        {
            cout <<y*y*pi-(y*y*acosl(x/2/y)-sqrtl(y*y-x*x/4)*x/2)*4 <<endl;

        }
    }
    else cout <<y*y*pi<<endl;
    //system("pause");
    return 0;
}