Use input() instead of raw_input(). [PEP 3111]
    
    raw_input() was renamed to input() in Python 3, and raw_input() was removed.
    For Python 2, apply a workaround so that we still execute the raw_input()
    function, since it behaves differently from input().
    
    See:
        https://www.python.org/dev/peps/pep-3111/