A. A Variety of Operationstime limit per test1 secondmemory limit per test256 megabytesinputstandard inputoutputstandard output  William has two numbers a and b initially both equal to zero. William mastered performing three different operations with them quickly. Before performing each operation some positive integer k is picked, which is then used to perform one of the following operations: (note, that for each operation you can choose a new positive integer k)  add number k to both a and b, or  add number k to a and subtract k from b, or  add number k to b and subtract k from a. Note that after performing operations, numbers a and b may become negative as well.William wants to find out the minimal number of operations he would have to perform to make a equal to his favorite number c and b equal to his second favorite number d.InputEach test contains multiple test cases. The first line contains the number of test cases t (1 \le t \le 10^4). Description of the test cases follows.The only line of each test case contains two integers c and d (0 \le c, d \le 10^9), which are William's favorite numbers and which he wants a and b to be transformed into.OutputFor each test case output a single number, which is the minimal number of operations which William would have to perform to make a equal to c and b equal to d, or -1 if it is impossible to achieve this using the described operations.ExampleInput
6
1 2
3 5
5 3
6 6
8 0
0 0
Output
-1
2
2
1
2
0
NoteLet us demonstrate one of the suboptimal ways of getting a pair (3, 5):  Using an operation of the first type with k=1, the current pair would be equal to (1, 1).  Using an operation of the third type with k=8, the current pair would be equal to (-7, 9).  Using an operation of the second type with k=7, the current pair would be equal to (0, 2).  Using an operation of the first type with k=3, the current pair would be equal to (3, 5). 
6
1 2
3 5
5 3
6 6
8 0
0 0

-1 2 2 1 2 0 
['math', '*800']