def day_to_string_en(day_dt):
    """
        :param day_dt: Day with format datetime
        :return: English word of the day (e.g., Monday, Tuesday, ...)
    """
    dict_res = {0: 'Monday', 1: 'Tuesday', 2: 'Wednesday', 3: 'Thursday',
                4: 'Friday', 5: 'Saturday', 6: 'Sunday'}
    return dict_res.get(day_dt.weekday(), "Invalid index of day")