def max_sequence_length_from_log(log):
    """
    Returns length of the longest sequence in the event log.
    :param log: event log.
    :return: max_seq_length.
    """

    max_seq_length = 0

    for sequence in log:
        max_seq_length_temp = 0
        for activity_ in sequence:
            max_seq_length_temp += 1
        if max_seq_length_temp > max_seq_length:
            max_seq_length = max_seq_length_temp

    return max_seq_length