#include <bits/stdc++.h>
using namespace std;
double a,b,c,p,s;
int main()
{
cin>>a>>b>>c;
if (a+b>c && b+c>a && c+b>a)
{
p=(a+b+c)/2;
s=sqrt(p*(p-a)*(p-b)*(p-c));
cout<<fixed<<setprecision(2)<<s;
}
else cout<<"Day khong la ba canh trong mot tam giac";
return 0;
}