#include <iostream>
#include <cmath>
using namespace std;
int main()
{double triangle(double,double,double);
 double a,b,c;
 cin>>a>>b>>c;
   while(a>0 && b>0 && c>0)
    {cout<<triangle(a,b,c)<<endl;
     cin>>a>>b>>c;
    }
 return 0;
}
  
double triangle(double a,double b,double c)
{double area;
 double s=(a+b+c)/2;
 area=sqrt(s*(s-a)*(s-b)*(s-c));
 return area; 
}