#include <iostream>
#include <cmath>

using namespace std;

const double pi = 4.0 * atan(1.0);

double S(double a, double b, double x)
{
	return pi * b * x / (2 * sqrt(1 - a * a / (4 * x * x)));
}

double solve(double a, double b)
{	
	const double eps = 1e-9;
	double l = a / 2;
	double u = a;

	while (u - l > eps) {
		double m1 = l + 1 * (u - l) / 3;
		double m2 = l + 2 * (u - l) / 3;
		double f1 = S(a, b, m1);
		double f2 = S(a, b, m2);
		if (f1 < f2) {
			u = m2;
		} else {
			l = m1;
		}
	}
	return S(a, b, (l + u) / 2);
}

int main()
{
	double a, b;
	while (cin >> a >> b) {
		cout << solve(a, b) << endl;
	}
}