说明：  现将举行一个餐会，让访客事先填写到达时间与离开时间，为了掌握座位的数目，必须先估计不同时间的最大访客数。
(Now hold a banquet, so that visitors fill out in advance the arrival time and departure time in order to keep the number of seats, you must first estimate the maximum number of visitors at different times.)