Minimum moves

You want to reach a destination but you decide that you can make moves in two directions only. If you are at position $(x,y)$, then you can move to $(x+1,y+1)$ or $(x+1,y)$. You must start your journey from $(0,0)$ and your destination is $(X,Y)$. Your task is to find the minimum number of moves that you require to reach the destination or if he cannot reach the destination.

Input format

• The first line contains an integer $T$ denoting the number of test cases.
• For each test case, there is a single line consisting of two integers $X$ and $Y$.

Output format

For each test case, print a single line denoting the minimum number of moves that you must take to reach the destination. Print -1 if you cannot reach the destination.

Constraints

$1\le T\le 1000$

$|X|,|Y|\le 1e9$

SAMPLE INPUT

 

1
1 0

SAMPLE OUTPUT

 

1

Explanation

He can take step from (x,y) to (x+1,y) .

So he can take step from (0,0) to (1,0).

Number of moves is 1 and is the optimal solution