description: <image>
  
  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)
  
    1. add number k to both a and b, or 
    2. add number k to a and subtract k from b, or 
    3. 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.
  
  Input
  
  Each test contains multiple test cases. The first line contains the number of test cases t (1 ≤ t ≤ 10^4). Description of the test cases follows.
  
  The only line of each test case contains two integers c and d (0 ≤ c, d ≤ 10^9), which are William's favorite numbers and which he wants a and b to be transformed into.
  
  Output
  
  For 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.
  
  Example
  
  Input
  
  
  6
  1 2
  3 5
  5 3
  6 6
  8 0
  0 0
  
  
  Output
  
  
  -1
  2
  2
  1
  2
  0
  
  Note
  
  Let 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). 
solution: import java.util.Scanner;
  
  public class e
  {
      public static void main(String[] args)  {
          Scanner scanner = new Scanner(System.in);
          int y = scanner.nextInt();
          de:
          for (int i = 0; i < y; i++) {
              long o = scanner.nextLong();
              long q = scanner.nextLong();
              if ((o-q) % 2 == 1 || (o-q) % 2 == -1){
                  System.out.println("-1");
                  continue;
              }
              if (o == 0 && q == 0){
                  System.out.println("0");
                  continue;
              }
              for (int j = 0; j < 5; j++) {
                  long p;
                  switch (j) {
                      case 0:
                          p = o - q / 2;
                          break;
                      case 1:
                          p = o;
                          break;
                      case 2:
                          p = o * -1;
                          break;
                      case 3:
                          p = q;
                          break;
                      case 4:
                          p = q * -1;
                          break;
                      default:
                          p = 0;
                          break;
                  }
                  for (int k = 0; k < 3; k++) {
                      long f = 0;
                      long g = 0;
                      switch (k){
                          case 0:
                              f = o - p;
                              g = q - p;
                              break;
                          case 1:
                              f = o + p;
                              g = q - p;
                              break;
                          case 2:
                              f = o - p;
                              g = q + p;
                              break;
                      }
                      if (f == 0 && g == 0){
                          System.out.println("1");
                          continue de;
                      }
                  }
              }
              System.out.println("2");
          }
      }
  }