#include <bits/stdc++.h>

using namespace std;
double a,b,c,s,p;
int main() { 

cin>>a>>b>>c;
if(a+b<=c or a+c<=b or b+c<=a)
{
    cout<<"Data Error!";
}
else{
p=(a+b+c)/2;
s=sqrt(p*(p-a)*(p-b)*(p-c));
printf("%.2f",s);
}
return 0;
}