description: You are given two integers n and m. Find the \operatorname{MEX} of the sequence n ⊕ 0, n ⊕ 1, …, n ⊕ m. Here, ⊕ is the [bitwise XOR operator](https://en.wikipedia.org/wiki/Bitwise_operation#XOR).
  
  \operatorname{MEX} of the sequence of non-negative integers is the smallest non-negative integer that doesn't appear in this sequence. For example, \operatorname{MEX}(0, 1, 2, 4) = 3, and \operatorname{MEX}(1, 2021) = 0. 
  
  Input
  
  The first line contains a single integer t (1 ≤ t ≤ 30 000) — the number of test cases.
  
  The first and only line of each test case contains two integers n and m (0 ≤ n, m ≤ 10^9).
  
  Output
  
  For each test case, print a single integer — the answer to the problem.
  
  Example
  
  Input
  
  
  5
  3 5
  4 6
  3 2
  69 696
  123456 654321
  
  
  Output
  
  
  4
  3
  0
  640
  530866
  
  Note
  
  In the first test case, the sequence is 3 ⊕ 0, 3 ⊕ 1, 3 ⊕ 2, 3 ⊕ 3, 3 ⊕ 4, 3 ⊕ 5, or 3, 2, 1, 0, 7, 6. The smallest non-negative integer which isn't present in the sequence i. e. the \operatorname{MEX} of the sequence is 4.
  
  In the second test case, the sequence is 4 ⊕ 0, 4 ⊕ 1, 4 ⊕ 2, 4 ⊕ 3, 4 ⊕ 4, 4 ⊕ 5, 4 ⊕ 6, or 4, 5, 6, 7, 0, 1, 2. The smallest non-negative integer which isn't present in the sequence i. e. the \operatorname{MEX} of the sequence is 3.
  
  In the third test case, the sequence is 3 ⊕ 0, 3 ⊕ 1, 3 ⊕ 2, or 3, 2, 1. The smallest non-negative integer which isn't present in the sequence i. e. the \operatorname{MEX} of the sequence is 0.
solution: import sys
  
  # file = open("error.txt", "r+")
  # file.truncate(0)
  # file.close()
  
  # def debug(*args):
  #     import sys
  #     if __debug__:
  #         orig_stdout = sys.stdout
  #         f = open('error.txt', 'a')
  #         sys.stdout = f
  #         for out in args:
  #             if isinstance(out, list) and all(isinstance(elem, list) for elem in out):
  #                 [[print(' '.join(list(map(str,s))))]for s in out]
  #             else:
  #                 sys.stdout.write(str(out)+' ')
  #         print()
  #         sys.stdout = orig_stdout
  #         f.close()
  
  t=int(input())
  for _ in range(t):
      n,m=list(map(int,sys.stdin.readline().strip().split()))
      if  n>m:
          print(0)
      else:
          bin_n=list(map(int,bin(n)[:1:-1]))
          bin_m=list(map(int,bin(m)[:1:-1]))
          # debug(bin_n)
          bin_m.append(0)
          changeable=[]
          min_diff=m-n
          diff_now=0
          for pos in range(len(bin_m)):
              if pos<len(bin_n) and bin_n[pos]==0:
                  changeable.append(2**pos)
                  diff_now+=changeable[-1]
              elif pos>=len(bin_n):
                  changeable.append(2**pos)
                  diff_now+=changeable[-1]
              if diff_now>min_diff:
                  break
          # debug(changeable,diff_now)
          for c in changeable[::-1]:
              if diff_now-c>min_diff:
                  diff_now-=c
          print(diff_now)
  