### Change

Time Limit : 1 Second

Memory Limit : 128 MB

Submission: 22

Solved: 9

Description
Sue is waiting in line at the grocery store. Being in a hurry, she wants to pay with exact change when she
gets to the front of the line. However, she does not know how much her items are going to cost; instead, she
only knows an upper bound C on their total cost. Given a list of the various coins Sue has in her pocket,
your goal is to determine the minimum number of coins she must take out in order to ensure that she can
make exact change for every amount from 1 to C.
Input
The input test file will contain multiple cases. Each test case begins with a single line containing two integers
C (where 1 ≤ C ≤ 1000000000) and m (where 1 ≤ m ≤ 1000), where C is the maximum amount for which
Sue must be able to make change, and m is the number of unique coin denominations Sue has in her pocket.
The next m lines each contain two numbers, vi (where 1 ≤ vi ≤ 1000) and ni (where 1 ≤ ni ≤ 1000), where
vi is the value of the ith coin denomination, and ni is the number of coins of that denomination that Sue
has in her pocket. Input is terminated by a single line containing the number 0; do not process this line.
Output
For each test case, either print a single line containing the number of coins Sue must use in order to make
exact change for all amounts up to C, or print “Not possible” if exact change cannot always be made with
any combination of coins in Sue’s pocket.
sample input
```4 2
2 1
1 3
9 3
1 5
8 2
7 1
0
```
sample output
```3
Not possible
```
hint
source
Stanford Local 2007
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