Cats & Dogs have become friends now. They are going to a picnic and they decided to sit together in groups to have their lunch.
There are N Cats & M Dogs. They can form any number of groups to sit together, subject to rules below.
Rules:

They will sit in a straight line
A Cat cannot sit beside another Cat or alone
A Dog cannot sit beside another Dog or alone
You need to find minimum number of groups they need to form. If no group can be formed then print -1.
Input Format:
First line of input will be a number of Test Cases T
Next T lines of input will contains two numbers N and M, delimited by space
Output Format:
Print minimum number of groups to be formed for each Test Case in new line
OR
Print -1 if no group can be formed
Constraints:
  1.  0<T<=10^6
  2.  0<N,M<=10^18

Example: Sample input and output

S.No.
Input
Output
1

2
5 5
1 3

1
-1
2

3
7 8
3 5
6 7

1
2
1