a = list(map(bool, map(int, list(input()))))[::-1]
b = list(map(bool, map(int, list(input()))))[::-1]

c = 0
for i in range(max(len(a), len(b))):
  if len(a) <= i or len(b) <= i:
    c += 2**i
  else:
    c += int(a[i]^b[i])*(2**i)
print(c)