A = input()
B = input()
A = A[::-1]
B = B[::-1]

ans = 0
for i in range(50):
	if len(A) > i:
		a = int(A[i])
	else:
		a = 0
	if len(B) > i:
		b = int(B[i])
	else:
		b = 0
	ans |= (a ^ b) << i
print(ans)