Solve the programming task below in a Python markdown code block.
Chef has N friends. Chef promised that he would gift a pair of shoes (consisting of one left shoe and one right shoe) to each of his N friends. Chef was about to go to the marketplace to buy shoes, but he suddenly remembers that he already had M left shoes.

What is the minimum number of extra shoes that Chef will have to buy to ensure that he is able to gift a pair of shoes to each of his N friends?

For example, if N = 2, M = 4, then Chef already has 4 left shoes, so he must buy 2 extra right shoes to form 2 pairs of shoes.

Therefore Chef must buy at least 2 extra shoes to ensure that he is able to get N = 2 pairs of shoes.

------ Input Format ------ 

- The first line contains a single integer T - the number of test cases. Then the test cases follow.
- The first line of each test case contains two integers N and M - the number of Chef's friends and the number of left shoes Chef has.

------ Output Format ------ 

For each test case, output the minimum number of extra shoes that Chef will have to buy to ensure that he is able to get N pairs of shoes.

------ Constraints ------ 

$1 ≤ T ≤ 100$
$1 ≤ N ≤ 100$
$0 ≤ M ≤ 100$

----- Sample Input 1 ------ 
3
2 4
6 0
4 3

----- Sample Output 1 ------ 
2
12
5

----- explanation 1 ------ 
Test Case 1: Discussed in the problem statement

Test Case 2: Chef initially has no left shoes. He must buy $6$ more left shoes and $6$ more right shoes to form $6$ pairs of shoes.

Test Case 3: Chef initially has $3$ left shoes. He must buy $1$ more left shoe and $4$ more right shoes to form $4$ pairs of shoes.