#include <bits/stdc++.h>

using namespace std;

int main()
{
	double a, b, c, p, m;

	cin >> a >> b >> c;

	p = (a + b + c) / 2;

	m = p * (p - a) * (p - b) * (p - c);

	cout << fixed << setprecision(2) << sqrt(m);

	return 0;
}