A = input()
B = input()
N = (len(A) if(len(A)>len(B)) else len(B))
A = A.zfill(N)
B = B.zfill(N)
ans = ''
for i in range(N):
    if(A[i]==B[i]):ans = ans+'0'
    else:ans = ans + '1'
print(int(ans,2))