#include<iostream>
#include<cmath>
#include <stdexcept>
using namespace std;
int main(){
    double s,p,a,b,c,d;
    cin>>a>>b>>c;
    p = 0.5*(a+b+c);
    s = p*(p-a)*(p-b)*(p-c);
    d = sqrt(s);
    printf("%.1f",d);
    return 0;
}