#include <iostream>
 
int main() 
{
    char current, last='\n';
   
    while(std::cin.get(current)) 
    {
        if (last == '\n' and current == '\n') 
        {
            std::cout << "Hello world!\n";
            return 0;
        }
        std::cout << current;
        last = current;
    }
}