#include <bits/stdc++.h>  
using namespace std;  
int main()  
{
    long long a,b,c;  
    double p;  
    scanf("%lld%lld%lld",&a,&b,&c);  
    p=(a+b+c)/2.0;  
    printf("%.1lf\n",sqrt(p*(p-a)*(p-b)*(p-c)));  
    return 0;  
}