a=input()
b=input()
if len(a)>len(b):
    n=len(a)
else:
    n=len(b)
a=a.zfill(n)
b=b.zfill(n)
d=''
for i in range(len(a)):
    if int(a[i])==1 and int(b[i])==1:
        d=d+('0')
    else:
        d=d+(str(int(a[i])+int(b[i])))

print(int(d,2))