[Usaco2005 mar]Yogurt factory 奶酪工厂

时间限制:5s      空间限制:64MB

题目描述

The cows have purchased a yogurt factory that makes world-famous Yucky Yogurt. Over the next N (1 <= N <= 10,000) weeks, the price of milk and labor will fluctuate weekly such that it will cost the company C_i (1 <= C_i <= 5,000) cents to produce one unit of yogurt in week i. Yucky's factory, being well-designed, can produce arbitrarily many units of yogurt each week. Yucky Yogurt owns a warehouse that can store unused yogurt at a constant fee of S (1 <= S <= 100) cents per unit of yogurt per week. Fortuitously, yogurt does not spoil. Yucky Yogurt's warehouse is enormous, so it can hold arbitrarily many units of yogurt. Yucky wants to find a way to make weekly deliveries of Y_i (0 <= Y_i <= 10,000) units of yogurt to its clientele (Y_i is the delivery quantity in week i). Help Yucky minimize its costs over the entire N-week period. Yogurt produced in week i, as well as any yogurt already in storage, can be used to meet Yucky's demand for that week.

 牛们收购了一个奶酪工厂,接下来的N个星期里,牛奶价格和劳力价格不断起伏.第i周,生产一个单位奶酪需要Ci(1≤Ci≤5000)便士.工厂有一个货栈,保存一单位奶酪,每周需要S(1≤S≤100)便士,这个费用不会变化.货栈十分强大,可以存无限量的奶酪,而且保证它们不变质.工厂接到订单,在第i周需要交付Yi(0≤Yi≤104)单位的奶酪给委托人.第i周刚生产的奶酪,以及之前的存货,都可以作为产品交付.请帮牛们计算这段时间里完成任务的最小代价.


输入格式

* Line 1: Two space-separated integers, N and S.

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

 
    第1行输入两个整数N和S.接下来N行输入Ci和Yi.


输出格式

* Line 1: Line 1 contains a single integer: the minimum total cost to satisfy the yogurt schedule. Note that the total might be too large for a 32-bit integer.

    输出最少的代价.注意,可能超过32位长整型.


样例输入

4 5
88 200
89 400
97 300
91 500


样例输出

126900

第1周生产200单位奶酪并全部交付;第2周生产700单位,交付400单位,有300单位;第3周交
付300单位存货.第4周生产并交付500单位.

提示

没有写明提示


题目来源

Gold