USACO 15.10 - 17.10

Nemogu prokuzit algoritam... Help plz


Problem 7: Allowance [Brian Dean, 2004]

As a reward for record milk production, Farmer John has decided to
start paying Bessie the cow a small weekly allowance. FJ has a set
of coins in N (1 <= N <= 20) different denominations, where each
denomination of coin evenly divides the next-larger denomination
(e.g., 1 cent coins, 5 cent coins, 10 cent coins, and 50 cent coins).
Using the given set of coins, he would like to pay Bessie at least
some given amount of money C (1 <= C <= 100,000,000) every week.
Please help him compute the maximum number of weeks he can pay
Bessie.

PROBLEM NAME: allow

INPUT FORMAT:

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

* Lines 2..N+1: Each line corresponds to a denomination of coin and
contains two integers: the value V (1 <= V <= 100,000,000) of
the denomination, and the number of coins B (1 <= B <=
1,000,000) of this denomation in Farmer John's possession.

SAMPLE INPUT (file allow.in):

3 6
10 1
1 100
5 120

INPUT DETAILS:

FJ would like to pay Bessie 6 cents per week. He has 100 1-cent coins,
120 5-cent coins, and 1 10-cent coin.

OUTPUT FORMAT:

* Line 1: A single integer that is the number of weeks Farmer John can
pay Bessie at least C allowance

SAMPLE OUTPUT (file allow.out):

111

OUTPUT DETAILS:

FJ can overpay Bessie with the one 10-cent coin for 1 week, then pay Bessie
two 5-cent coins for 10 weeks and then pay Bessie one 1-cent coin and one
5-cent coin for 100 weeks.