def reverse_string(input):
    """
    Return reversed input string
    
    Examples:
       reverse_string("abc") returns "cba"
    
    Args:
      input(str): string to be reversed
    
    Returns:
      a string that us reversed of input
    """
    if len(input) == 0:
        return ""
    else:
        first_char = input[0]
        the_rest = slice(1, None)
        sub_string = input[the_rest]
        reversed_substring = reverse_string(sub_string)
        return reversed_substring + first_char