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

}