def hhmmss_to_seconds_since_midnight(time_int):
    """
        Convert  HH:MM:SS into seconds since midnight.
        For example "01:02:03" returns 3723. The leading zero of the hours may be
        omitted. HH may be more than 23 if the time is on the following day.
        :param time_int: HH:MM:SS string. HH may be more than 23 if the time is on the following day.
        :return: int number of seconds since midnight
        """
    time_int = int(''.join(time_int.split(':')))
    hour = time_int // 10000
    minute = (time_int - hour * 10000) // 100
    second = time_int % 100
    return hour * 3600 + minute * 60 + second