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