def channel_to_frequency(itu_channel):
    """ Convert frequency in GHz to ITU DWDM channel in C-band

    >>> channel_to_frequency(0)
    193100
    >>> channel_to_frequency(-7)
    192750
    >>> channel_to_frequency(9)
    193550
    """
    return int(193100 + 50 * itu_channel)
