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