#include<bits/stdc++.h>
#include<cstdio>
#include<cmath>
using namespace std ;
int main (){
    double a,b,c,p,d,e;
    cin>>a>>b>>c;
    p=(a+b+c)/2;
    d=p*(p-a)*(p-b)*(p-c);
    e=pow(d,0.5);
    printf("%.1lf",e);
    return 0;
}