[USACO08NOV] Buying Hay S
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 $H(1 \leq H \leq 50000)$ 磅干草。 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 $H$ 磅干草。
\* 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
\* Line 1: A single integer representing the minimum cost FJ needs to pay to obtain at least H pounds of hay.
2 15 3 2 5 3
FJ can buy three packages from the second supplier for a total cost of 9.