s=input()
t=input()
ans=""
if len(s)<len(t):s,t=t,s
nt="0"*(len(s)-len(t))+str(t)
# print(nt)
for i in range(len(s)):
	ans+=str(int(s[i])^ int(nt[i]))
# print(ans)
print(int(ans,2))