Description

胖老鼠准备了M磅的猫粮，准备和看守仓库的猫交易，仓库里有他最喜欢的食物，爪哇豆JavaBeans。
这个仓库有n个房间，第i个房间含有J[i]磅的JavaBeans，交换这些JavaBeans需要F[i]磅的猫食。在交换过程中胖老鼠不必交易房间里的所有JavaBean，相反，如果付给F[i]*a%磅的猫粮，他可能会得到J[i]*a%磅的JavaBeans。现在胖老鼠把这项作业分配给你：告诉他能得到的最大数量的JavaBeans。

FatMouse prepared M pounds of cat food, ready to trade with the cats guarding the warehouse containing his favorite food, JavaBean.
The warehouse has N rooms. The i-th room contains J[i] pounds of JavaBeans and requires F[i] pounds of cat food. FatMouse does not have to trade for all the JavaBeans in the room, instead, he may get J[i]* a% pounds of JavaBeans if he pays F[i]* a% pounds of cat food. Here a is a real number. Now he is assigning this homework to you: tell him the maximum amount of JavaBeans he can obtain.

Input Format

输入由多个测试用例组成。每个测试用例以包含两个非负整数M和N的行开始。M表示胖老鼠具有的猫粮数，N表示房间房间数。后面N行，每个行分别包含两个非负整数J[i]和F[i]，最后一个测试用例后面是两到-1,表示输入结束。所有的整数都不大于1000。

Output Format

对于每个测试用例，在一行中打印一个实数，最多精确到小数点后3位，这是胖老鼠FatMouse可以获得的JavaBean的最大数量。

5 3
7 2
4 3
5 2
20 3
25 18
24 15
15 10
-1 -1

13.333
31.500

Hint

-李勇周赛

Source