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Burglar and Matches
盗贼和火柴
描述:
A burglar got into a matches warehouse and wants to steal as many matches as possible. In the warehouse there are m containers, in the i-th container there are ai matchboxes, and each matchbox contains bi matches. All the matchboxes are of the same size. The burglar's rucksack can hold n matchboxes exactly. Your task is to find out the maximum amount of matches that a burglar can carry away. He has no time to rearrange matches in the matchboxes, that's why he just chooses not more than n matchboxes so that the total amount of matches in them is maximal.
一个盗贼进入了一个火柴仓库想要尽可能偷到最多的火柴。在仓库里有m个容器,在第i个容器里有ai个火柴盒,每个火柴盒里有bi个火柴。所有的火柴盒都是一样的大小。盗贼的帆布背包只能装n个火柴盒。你的任务是这个盗贼能够带走火柴数量的最大值。他没有时间重新排列在火柴盒里的火柴,这就是为什么他只选择不超过 n 个火柴盒,以使其中的火柴的数量是最大的。
输入:
The first line of the input contains integer n (1 ≤ n ≤ 2·108) and integer m (1 ≤ m ≤ 20). The i + 1-th line contains a pair of numbers ai and bi (1 ≤ ai ≤ 108, 1 ≤ bi ≤ 10). All the input numbers are integer.
第一行输入包括整数n(1 ≤ n ≤ 2·108)和整数m(1 ≤ m ≤ 20)。第i+1行包括一组数字ai和bi(1 ≤ ai ≤ 108, 1 ≤ bi ≤ 10)。所有输入的数字都是整数。
输出:
Output the only number — answer to the problem.
输出只有一个数字--问题的答案。
样例输入:
7 3 5 10 2 5 3 6
复制
样例输出:
62