Problem7181--ABC223 —— C - Doukasen

7181: ABC223 —— C - Doukasen

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Time Limit : 1.000 sec  Memory Limit : 256 MiB

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Description

We have $N$ fuses connected in series. The i-th fuse from the left has a length of $A_i$ centimeters and burns at a constant speed of $B_i$ centimeters per second.
Consider igniting this object from left and right ends simultaneously. Find the distance between the position where the two flames will meet and the left end of the object.

Input

Input is given from Standard Input in the following format:
$N$
$A_1\ B_1$
$A_2\ B_2$
$\vdots$
$A_N\ B_N$

Output

Print the distance between the position where the two flames will meet and the left end of the object, in centimeters (print just the number).
输出保持 $7$ 位小数点。

Constraints

$1≤N≤10^5$
$1 \leq A_i,B_i \leq 1000$
All values in input are integers.

Sample 1 Input 

3
1 1
2 1
3 1

Sample 1 Output 

3.0000000
The two flames will meet at 3 centimeters from the left end of the object.

Sample 2 Input 

3
1 3
2 2
3 1

Sample 2 Output 

3.8333333

Sample 3 Input 

5
3 9
1 2
4 6
1 5
5 3

Sample 3 Output 

8.9166667

Source/Category

 
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