#include<iostream>
#include<cmath>
using namespace std;
int main()
{
double triangle(double,double,double);//函数声明
double a,b,c;
cin>>a>>b>>c; //输入3个边
while(a>0 && b>0 && c>0)
{
cout<<triangle(a,b,c)<<endl; //输出三角形的面积
cin>>a>>b>>c; //输入3个边
}
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;
}