S = eval(input())

T = eval(input())

if len(S) != len(T): quit()

sum = 0

for i in range(len(S)):

    if T[i] != S[i]:

        sum = sum + 1

print(sum)


def main():

    

    s = eval(input())

    t = eval(input())



    count = 0

    

    for i in range(len(s)):

        if s[i] != t[i]:

            count += 1

            

    print(count)    



if __name__ == "__main__":

    main()
S = eval(input())
T = eval(input())
if len(S) != len(T):
    quit()
sum = 0
for i in range(len(S)):
    if T[i] != S[i]:
        sum = sum + 1
print(sum)

def main():
    s = eval(input())
    t = eval(input())
    count = 0
    for i in range(len(s)):
        if s[i] != t[i]:
            count += 1
    print(count)


if __name__ == "__main__":
    main()

-S = eval(input()) -T = eval(input()) -if len(S) != len(T): -    quit() -sum = 0 -for i in range(len(S)): -    if T[i] != S[i]: -        sum = sum + 1 -print(sum) +def main(): +    s = eval(input()) +    t = eval(input()) +    count = 0 +    for i in range(len(s)): +        if s[i] != t[i]: +            count += 1 +    print(count) + + +if __name__ == "__main__": +    main()