Untitled

#include <iostream>
#include <cmath>
using namespace std;

int main()
{
	double a, b ,c, s = 0,p = 0;
	cin >> a >> b >> c;
	p = (a + b + c) / 2;
	s = sqrt(p * (p - a) * (p - b) * (p - c));
	cout << s;
}