#include<bits/stdc++.h> using namespace std; int main() { double a, b, c, p, m;

cin >> a >> b >> c;

p = (a + b + c) / 2;

m = p * (p - a) * (p - b) * (p - c);

cout << fixed << setprecision(2) << sqrt(m);



return 0;

}