Untitled

#include <iostream>
#include <cmath>

using namespace std;

int main() {
	double a, b, c, p, s;
	cin >> a >> b >> c;
	p = (a + b + c) / 2;
	s = sqrt(p * (p - a) * (p - b) * (p - c));
	cout << s << endl;
}