#include <iostream>
#include <cstring>
#include <cmath>
#include <algorithm>
#include <iomanip>
using namespace std;
int main()
{
	double sum,p;
	int a,b,c;
	cin >> a >> b >> c;
	p = (a + b + c) / 2;
	sum = p * (p - a) * (p - b) * (p - c);
	sum = sqrt(sum);
	cout << fixed << setprecision(1) << sum << endl;
	return 0;
}