### 1517 Fat Mouse Trade

#### 时间限制 : 2000/1000 MS(Java/Others) | 内存限制 : 65536/32768 KB(Java/Others)

#### 提交数 : 3655 | 通过数 : 530

## 题目描述

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.

## 输入要求

The input consists of multiple test cases. Each test case begins with a line containing two non-negative integers M and N. Then N lines follow, each contains two non-negative integers J[i] and F[i] respectively. The last test case is followed by two -1's. All integers are not greater than 1000.

## 输出要求

For each test case, print in a single line a real number accurate up to 3 decimal places, which is the maximum amount of JavaBeans that FatMouse can obtain.

## 输入样例

5 3 7 2 4 3 5 2 -1 -1

## 输出样例

13.333

## 提示

结合结构体，会使处理过程更简洁:)

<=1000

## 来源

`Zhejiang Provincial Programming Contest 2004`