a = list(map(bool, map(int, list(input()))))[::-1]
b = list(map(bool, map(int, list(input()))))[::-1]
if len(a) < len(b):
  a.append(False)
elif len(a) > len(b):
  b.append(False)
c = 0
for i in range(len(a)):
  c += int(a[i]^b[i])*(2**i)
print(c)