def get_length(crf2subtype2bitmask):
    """
    Calculates the alignment length for the breakpoint bitmask mapping.

    :param crf2subtype2bitmask: mapping between CRF ids and a mapping of subtypes to breakpoint interval list (aligned):
        {id: {subtype: [(start, stop), ...], ...}, ..}
    :type crf2subtype2bitmask: dict
    :return: alignment length
    :rtype: int
    """
    return len(next(iter(next(iter(crf2subtype2bitmask.values())).values())))
