def mac_hex(number):
    """Convert integer to hexadecimal for incrementing MAC addresses.

    :param number: Integer number less than 100.
    :type number: int

    :returns: 2-digit hexadecimal representation of the input number.
    :rtype: str
    """

    temp = hex(number)[2:]
    if number < 16:
        temp = "0{0}".format(temp)
    elif number > 99:
        raise NotImplementedError(
            "Incrementing MAC addresses only implemented up to 99.")
    else:
        pass
    return temp