from datetime import datetime


def datetime_month_fistday( date : datetime ):
    """
    Get the first day of the month at 00:00:00.000
    :param date: Date
    :type date: datetime
    
    :return: The date setted with the first day of month
    :rtype: datetime
    """
    return date.replace(day=1, hour = 0, minute = 0, second=0, microsecond=0 )