# [Usaco2008 Nov]Time Management 时间管理

时间限制：5s 空间限制：64MB

### 题目描述

Ever the maturing businessman, Farmer John realizes that he must manage his time effectively. He has N jobs conveniently numbered 1..N (1 <= N <= 1,000) to accomplish (like milking the cows, cleaning the barn, mending the fences, and so on). To manage his time effectively, he has created a list of the jobs that must be finished. Job i requires a certain amount of time T_i (1 <= T_i <= 1,000) to complete and furthermore must be finished by time S_i (1 <= S_i <= 1,000,000). Farmer John starts his day at time t=0 and can only work on one job at a time until it is finished. Even a maturing businessman likes to sleep late; help Farmer John determine the latest he can start working and still finish all the jobs on time.

N个工作,每个工作其所需时间,及完成的Deadline,问要完成所有工作,最迟要什么时候开始.

### 输入格式

* Line 1: A single integer: N

* Lines 2..N+1: Line i+1 contains two space-separated integers: T_i and S_i

### 输出格式

* Line 1: The latest time Farmer John can start working or -1 if Farmer John cannot finish all the jobs on time.

### 样例输入

4 3 5 8 14 5 20 1 16 INPUT DETAILS: Farmer John has 4 jobs to do, which take 3, 8, 5, and 1 units of time, respectively, and must be completed by time 5, 14, 20, and 16, respectively.

### 样例输出

2 OUTPUT DETAILS: Farmer John must start the first job at time 2. Then he can do the second, fourth, and third jobs in that order to finish on time.

### 提示

没有写明提示

### 题目来源

Silver