CF479C Exams

学生进行期末考试，每个考试时间在$a_i$，Valera和老师约定提前于时间$b_i$进行考试，要求所有考试按照$a_i$的顺序，求Valera最早哪个时间可以结束考试。

第一行一个整数，考试数目nnn。接下来n+1行每行两个整数代表$a_i$和$b_i$。

一个整数，代表最小结束时间。 ##### 数据规模 n

In the first sample Valera first takes an exam in the second subject on the first day (the teacher writes down the schedule date that is 3). On the next day he takes an exam in the third subject (the teacher writes down the schedule date, 4), then he takes an exam in the first subject (the teacher writes down the mark with date 5). Thus, Valera takes the last exam on the second day and the dates will go in the non-decreasing order: 3, 4, 5. In the second sample Valera first takes an exam in the third subject on the fourth day. Then he takes an exam in the second subject on the fifth day. After that on the sixth day Valera takes an exam in the first subject.