Piggy-Bank

Time Limit: 2 Seconds
Memory Limit: 65536 KB

Before ACM can do anything, a budget must be prepared and the necessary financial
support obtained. The main income for this action comes from Irreversibly Bound
Money (IBM). The idea behind is simple. Whenever some ACM member has any small
money, he takes all the coins and throws them into a piggy-bank. You know that
this process is irreversible, the coins cannot be removed without breaking the
pig. After a sufficiently long time, there should be enough cash in the piggy-bank
to pay everything that needs to be paid.

But there is a big problem with piggy-banks. It is not possible to determine
how much money is inside. So we might break the pig into pieces only to find
out that there is not enough money. Clearly, we want to avoid this unpleasant
situation. The only possibility is to weigh the piggy-bank and try to guess
how many coins are inside. Assume that we are able to determine the weight of
the pig exactly and that we know the weights of all coins of a given currency.
Then there is some minimum amount of money in the piggy-bank that we can guarantee.
Your task is to find out this worst case and determine the minimum amount of
cash inside the piggy-bank. We need your help. No more prematurely broken pigs!

**Input**

The input consists of T test cases. The number of them (T) is given on the first
line of the input. Each test case begins with a line containing two integers
E and F. They indicate the weight of an empty pig and of the pig filled with
coins. Both weights are given in grams. No pig will weigh more than 10 kg, that
means 1 <= E <= F <= 10000. On the second line of each test case, there
is an integer number N (1 <= N <= 500) that gives the number of various
coins used in the given currency. Following this are exactly N lines, each specifying
one coin type. These lines contain two integers each, Pand W (1 <= P <=
50000, 1 <= W <=10000). P is the value of the coin in monetary units,
W is it's weight in grams.

**Output**

Print exactly one line of output for each test case. The line must contain the
sentence "The minimum amount of money in the piggy-bank is X." where
X is the minimum amount of money that can be achieved using coins with the given
total weight. If the weight cannot be reached exactly, print a line "This
is impossible.".

**Sample Input**

3

10 110

2

1 1

30 50

10 110

2

1 1

50 30

1 6

2

10 3

20 4

**Sample Output**

The minimum amount of money in the piggy-bank is 60.

The minimum amount of money in the piggy-bank is 100.

This is impossible.

Source:

**Central Europe 1999**
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