Chandu and his toy stack
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## Data Structures, Greedy algorithm

Problem
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After setting up the area. Chandu wanted all his toys to be stacked there in that area. So that all of them are accessible easily. Currently, He is having N stacks of toys each with height $H_1,H_2...H_n$ (assuming all toys are of same height).Chandu did not like the configuration much and want to change the height of each stack. To increase the height of a particular stack he can add some toys to it and to decrease the height he can take out some toys from that stack. Chandu, knows that he requires X units of effort for putting up an item onto the stack and Y units of effort for removing it. Help, chandu in setting up his toys.

Input:

First Line of input contains an integer t, which is the number of test cases. then, t lines follow where first line of each test case contains three integers N, X and Y then N lines follow containing two integers each $a[i]$ and $b[i]$ (Initial height of $i\;th$ stack and final height of $i\;th$ stack.)

Output:

Output an integer which is the minimum effort required.

NOTE: he just need to make stacks of given height. Not necessarily each stack should be made from its corresponding stack.

Constraints:

$1 \le t \le 100,$
$1 \le N \le 10^5,$
$1 \le a[i],b[i] \le 10^6$

SAMPLE INPUT
1
3 6 4
3 1
1 2
1 2

SAMPLE OUTPUT
10

Explanation

Here, He is having 3 stacks initially of height $3,1$ and 1 He can take out one toy from first stack to get a stack with two toys with 4 units of effort. He can put toy on second stack to get a stack with two toys with 6 units of effort. Total effort = $10$ units. After the two operations he will have three stacks with required heights.

Time Limit: 1.0 sec(s) for each input file.
Memory Limit: 256 MB
Source Limit: 1024 KB

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