小张子作为学生会的一名，要将足够多的会场安排给一批活动，同事又希望所使用会场

尽可能的少。

第一行为一个正整数 k (1< k< 10000)，表示待安排的活动的个数。接下来有 k 行，

每行均有两个正整数，表示第 k 个活动的开始时间和结束时间，时间计算从 0 开始，每分

钟多 1。

-Zhang s son as a student, to a sufficient number of venues to arrange a number of activities, colleagues and want to use the venue

As little as possible.

The first line a positive integer k (1 <　k <　10000), indicates the number of events to be arranged. Then there are k rows,

Each row has two positive integer representing the start time of the k-th activity and end time, time calculation starts　0 per minute

More than 1 clock.