tj

#include<bits/stdc++.h>
#include<cmath>
using namespace std;
double s,a,b,c,p;
int main()
{
cin>>a>>b>>c;
p = (a+b+c)/2;
s = sqrt(p*(p-a)(p-b)(p-c));
printf("%.2f",s);
return 0;
}