def shorter(s1, s2):
    """ (str, str) -> int
    
    Return -1 if string s1 is shorter than string s2, 1 if it is longer,
    and 0 if they have equal length.
    """
    
    if len(s1) < len(s2):
        return -1
    elif len(s1) > len(s2):
        return 1
    else:
        return 0