#include<bits/stdc++.h>
#include <cmath>
int main()  
{  
    double a, b, c, p, d;  
    scanf("%lf %lf %lf", &a, &b, &c);  
    p = (a + b + c) * 0.5;  
    d = p * (p - a) * (p - b) * (p - c);  
    d = sqrt(d);  
    printf("%.1f", d);  
    return 0;  
}