#include <iostream>
#include <cmath>

using namespace std;

const double pi = 4.0 * atan(1.0);

double solve(double a, double b)
{
	return pi * a * b / 2;
}

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