8216: Milk Scheduling

内存限制:128 MB 时间限制:1 S 标准输入输出
题目类型:传统 评测方式:文本比较 上传者:
提交:24 通过:10

题目描述

 Farmer John has N cows that need to be milked (1 <= N <= 10,000), each of which takes only one unit of time to milk.
 Being impatient animals, some cows will refuse to be milked if Farmer John waits too long to milk them. More specifically, cow i produces g_i gallons of milk (1 <= g_i <= 1000), but only if she is milked before a deadline at time d_i (1 <= d_i <= 10,000). Time starts at t=0, so at most x total cows can be milked prior to a deadline at time t=x. 
Please help Farmer John determine the maximum amount of milk that he can obtain if he milks the cows optimally. 

输入格式

 Line 1: The value of N. * Lines 2..1+N: Line i+1 contains the integers g_i and d_i. SAMPLE INPUT (file msched.in): 4 10 3 7 5 8 1 2 1 INPUT DETAILS: There are 4 cows. The first produces 10 gallons of milk if milked by time 3, and so on. 

输出格式

* Line 1: The maximum number of gallons of milk Farmer John can obtain. 

输入样例 复制

4
10 3
7 5
8 1
2 1

输出样例 复制

25

数据范围与提示

INPUT DETAILS: There are 4 cows. The first produces 10 gallons of milk if milked by time 3, and so on. 
OUTPUT FORMAT: * Line 1: The maximum number of gallons of milk Farmer John can obtain. 
SAMPLE OUTPUT (file msched.out): 
25
 OUTPUT DETAILS: Farmer John milks cow 3 first, giving up on cow 4 since she cannot be milked by her deadline due to the conflict with cow 3. Farmer John then milks cows 1 and 2.