A = input()
B = input()

N = max(len(A), len(B))
strA = str(A).zfill(N)
strB = str(B).zfill(N)

ans = ""
for i in range(N):
    if strA[i] == strB[i]:
        ans += "0"
    else:
        ans += "1"

ansin = int(ans, 2)
print(ansin)