#include <iostream>
#include <cmath>
int main()
{
double a, b, c, S, P;
cin >> a >> b >> c;
P = (a + b + c) / 2.0;
S = sqrt(P * (P - a) * (P - b) * (P - c));
cout << S;
return 0;
}
#include <iostream>
#include <cmath>
int main()
{
double a, b, c, S, P;
cin >> a >> b >> c;
P = (a + b + c) / 2.0;
S = sqrt(P * (P - a) * (P - b) * (P - c));
cout << S;
return 0;
}