Package for this problem was not updated by the problem writer or Codeforces administration after we’ve upgraded the judging servers. To adjust the time limit constraint, solution execution time will be multiplied by 2. For example, if your solution works for 400 ms on judging servers, then value 800 ms will be displayed and used to determine the verdict.

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B. Burglar and Matches

time limit per test

0.5 secondmemory limit per test

64 megabytesinput

standard inputoutput

standard outputA 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 *a*_{i} matchboxes, and each matchbox contains *b*_{i} 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.

Input

The first line of the input contains integer *n* (1 ≤ *n* ≤ 2·10^{8}) and integer *m* (1 ≤ *m* ≤ 20). The *i* + 1-th line contains a pair of numbers *a*_{i} and *b*_{i} (1 ≤ *a*_{i} ≤ 10^{8}, 1 ≤ *b*_{i} ≤ 10). All the input numbers are integer.

Output

Output the only number — answer to the problem.

Examples

Input

7 3

5 10

2 5

3 6

Output

62

Input

3 3

1 3

2 2

3 1

Output

7

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