#include <bits/stdc++.h>
using namespace std;
int main() {
      int a, b, c;
      cin >> a >> b >> c;
      double p = (double) (a+b+c)/2;
      double s = sqrt(p*(p-a)*(p-b)*(p-c));
      cout << fixed << setprecision(2) << s;
	
}