Cricket Qualification

In a cricket tournament a team is finding it tough to qualify for playoffs. They needs a minimum of X more points to qualify for playoffs in their remaining Y matches. A win, tie and loss in a match will yield 2,1,0 points respectively to a team.

You are assigned a task to find the minimum number of matches team needs to win to qualify for playoffs. It is guaranteed that team will qualify for playoffs if they win all their remaining Y matches.
        
       Input:-2
10 5
1 5
       Input Description: first line will contain T, number of testcases. Then The testcases follow.
-each testcase contains of a single line of input, two space separated integers X,Y 
       Output: 5
0
       Output Description: For each testcase, output in a single line the minimum number of matches team must win to qualify for playoffs. 
       Constraints: 1<=T<=10000
1<=X<=100
1<=Y<=100
1<=X<=2?Y
       Explanation: -In first case X=10 and Y=5, so the team needs 10 points from remaining 5 matches to qualify for playoffs. It is only possible if they win all their remaining 5 matches.

-In second case X=1 and Y=5, so the team needs 1 points from their remaining 5 matches to qualify for playoffs. It can be done if they tie any one of their 5 matches and lose the remaining 4. So they need to win 0 matches.