#include <iostream>
#include <vector>
#include <cmath>
#include <algorithm>
#include <set>
#include <unordered_map>
#include <map>
#include <string>
using namespace std;
double n, l;
const double pi = 3.1415926535;
double len(double k1, double g1)
{
    return sqrt(g1 * g1 - k1 * k1);
}
double sqrci(double r)
{
    return pi * r * r;
}

int main()
{
    cin >> n >> l;
    if(l <= (n / 2))
    {
        cout << sqrci(l);
    }
    double x = len(n / 2, l);
    double ang = asin(x / l);
    ang *= 2;
    double sqrsec = (ang / (2 * pi)) * sqrci(l);
    double sqrtry = x * (n / 2);
    cout << sqrci(l) - 4 * (sqrsec - sqrtry);

}