#include <iostream>
#include<math.h>
using namespace std;
int main()
{
	int a, b, c;
	cin >> a >> b >> c;
	a, b, c >= 0 && a, b, c <= 1000;
	 double p,s;
	p = 0.5* (a + b + c);
	s = sqrt(p * (p - a) * (p - b) * (p - c));

	printf("%.1lf",s);
	system("pause");
		return 0;
};