A = input()
B = input()

if len(A) < len(B):
	A = '0' * (len(B) - len(A)) + A
else:
	B = '0' * (len(A) - len(B)) + B

ans = ''
for a, b in zip(A, B):
	if a == b == '0' or a == b == '1':
		ans += '0'
	else:
		ans += '1'
print(int(ans, 2))