from re import match


def valid_input(instructions):
    """
    Validate input to be a multi-line string containing directions [UDLR]+
    :param instructions: Multiline string input
    :return: Boolean value whether input is valid
    """
    m = match(r'[UDLR]+', ''.join(instructions))
    return m is not None and m.span() == (0, sum(len(i) for i in instructions))