# P2918 [USACO08NOV]买干草Buying Hay

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• 题目提供者 FarmerJohn2
• 评测方式 云端评测
• 标签 背包 贪心 USACO 2008
• 难度 普及/提高-
• 时空限制 1000ms / 128MB
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## 题目描述

Farmer John is running out of supplies and needs to purchase H (1 <= H <= 50,000) pounds of hay for his cows.

He knows N (1 <= N <= 100) hay suppliers conveniently numbered 1..N. Supplier i sells packages that contain P_i (1 <= P_i <= 5,000) pounds of hay at a cost of C_i (1 <= C_i <= 5,000) dollars. Each supplier has an unlimited number of packages available, and the packages must be bought whole.

Help FJ by finding the minimum cost necessary to purchase at least H pounds of hay.

约翰的干草库存已经告罄，他打算为奶牛们采购$H(1 \leq H \leq 50000)$镑干草.

他知道$N(1 \leq N\leq 100)$个干草公司，现在用$1$到$N$给它们编号.第$i$公司卖的干草包重量 为$P_i (1 \leq P_i \leq 5,000)$ 磅，需要的开销为$C_i (1 \leq C_i \leq 5,000)$ 美元.每个干草公司的货源都十分充足， 可以卖出无限多的干草包.

帮助约翰找到最小的开销来满足需要，即采购到至少$H$镑干草.

## 输入输出格式

输入格式：

* Line 1: Two space-separated integers: N and H

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

输出格式：

* Line 1: A single integer representing the minimum cost FJ needs to pay to obtain at least H pounds of hay.

## 输入输出样例

输入样例#1： 复制
2 15
3 2
5 3

输出样例#1： 复制
9


## 说明

FJ can buy three packages from the second supplier for a total cost of 9.

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