e

#include <bits/stdc++.h>
using namespace std;
void f(int a)
{

}
int main()
{
double b,c,p,a;
double s;
cin>>a>>b>>c;
p=(a+b+c)/2;
s=sqrt(p*(p-a)(p-b)(p-c));
cout<<fixed<<setprecision(2)<<s<<endl;
return 0;
}