import sys
def input():
    return sys.stdin.readline().rstrip()
from collections import deque
def main():
    a = int(input())
    p = 0
    A = 0
    while a:
        A += a%10*2**p
        a //= 10
        p += 1
    b = int(input())
    p = 0
    B = 0
    while b:
        B += b%10*2**p
        b //= 10
        p += 1
    print(A^B)
if __name__ == "__main__":
    main()