#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;
}
}
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