import io
import sys

_INPUT = """\
6
10
100
111
111
10100
1011
"""

def solve(test):
  A=input()
  B=input()
  ans=0
  if len(A)>len(B): B='0'*(len(A)-len(B))+B
  elif len(A)<len(B): A='0'*(len(B)-len(A))+A
  N=len(A)
  for i in range(N):
    if A[N-1-i]!=B[N-1-i]: ans+=1<<(i)
  if test==0:
    print(ans)
  else:
    return None

def random_input():
  from random import randint,shuffle
  N=randint(1,10)
  M=randint(1,N)
  A=list(range(1,M+1))+[randint(1,M) for _ in range(N-M)]
  shuffle(A)
  return (" ".join(map(str, [N,M]))+"\n"+" ".join(map(str, A))+"\n")*3

def simple_solve():
  return []

def main(test):
  if test==0:
    solve(0)
  elif test==1:
    sys.stdin = io.StringIO(_INPUT)
    case_no=int(input())
    for _ in range(case_no):
      solve(0)
  else:
    for i in range(1000):
      sys.stdin = io.StringIO(random_input())
      x=solve(1)
      y=simple_solve()
      if x!=y:
        print(i,x,y)
        print(*[line for line in sys.stdin],sep='')
        break

#0:提出用、1:与えられたテスト用、2:ストレステスト用
main(0)