Go to movies

Time Limit: 2000/1000 MS (Java/Others)

Memory Limit: 65536/65536 K (Java/Others)

Description

Winter holiday is coming!As the monitor, LeLe plans to go to the movies.
Because the winter holiday tickets are pretty expensive, LeLe decideds to try group-buying.

Input

There are multiple test cases, about $20$ cases. The first line of input contains two integers $n,m(1 \leq n,m \leq 100)$. $n$ indicates the number of the students. $m$ indicates how many cinemas have offered group-buying.

For the $m$ lines,each line contains two integers $a_i,b_i(1 \leq ai,bi \leq 100)$, indicating the choices of the group buying cinemas offered which means you can use $b_i$ yuan to buy $a_i$ tickets in this cinema.

Output

For each case, please help LeLe **choose a cinema** which costs the least money. Output the total money LeLe should pay.

Sample Input

3 2 2 2 3 5

Sample Output

4
Hint
LeLe can buy four tickets with four yuan in cinema 1.

Hint

hujie

Source

BestCoder Round #34

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