#include <bits/stdc++.h>
using namespace std;
double a,b,c,p,s;
bool kt;
int main()
{
cin>>a>>b>>c;
if ((a>0) and (b>0) and (c>0) and (a+b>c) and (a+c>b) and (b+c>a))
{
kt=false;
if (a*a==b*b+c*c) kt=true;
if (b*b==a*a+c*c) kt=true;
if (c*c==a*a+b*b) kt=true;
if (kt==false) cout<<"Day khong la ba canh trong mot tam giac vuong";
else {
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 vuong";
}