#include <iostream>
using namespace std;
double Average(double,double);

int main()
{
	double a,b,average;
	cout<<"Please enter two number:\n";
	while (cin>>a>>b&&a!=0&&b!=0)
	{
		average=Average(a,b);
		cout<<"Harmonic average: "<<average<<endl;
		cout<<"Please enter two number:\n";
		continue;
	}
	cout<<"Bye!!";
	return 0;
}

double Average(double a,double b)
{
	double average;
	average=2*a*b/(a+b);
	return average;
}