import sys



readline = sys.stdin.readline

MOD = 10 ** 9 + 7

INF = float('INF')

sys.setrecursionlimit(10 ** 5)





def main():

    s = eval(input())

    t = eval(input())

    ans = 0



    for ch1, ch2 in zip(s, t):

        if ch1 != ch2:

            ans += 1



    print(ans)





if __name__ == '__main__':

    main()

s = eval(input())

t = eval(input())



ans = 0

for char_s, char_t in zip(s, t):

    if char_s != char_t:

        ans += 1



print(ans)
import sys

readline = sys.stdin.readline
MOD = 10**9 + 7
INF = float("INF")
sys.setrecursionlimit(10**5)


def main():
    s = eval(input())
    t = eval(input())
    ans = 0
    for ch1, ch2 in zip(s, t):
        if ch1 != ch2:
            ans += 1
    print(ans)


if __name__ == "__main__":
    main()

s = eval(input())
t = eval(input())
ans = 0
for char_s, char_t in zip(s, t):
    if char_s != char_t:
        ans += 1
print(ans)

-import sys - -readline = sys.stdin.readline -MOD = 10**9 + 7 -INF = float("INF") -sys.setrecursionlimit(10**5) - - -def main(): -    s = eval(input()) -    t = eval(input()) -    ans = 0 -    for ch1, ch2 in zip(s, t): -        if ch1 != ch2: -            ans += 1 -    print(ans) - - -if __name__ == "__main__": -    main() +s = eval(input()) +t = eval(input()) +ans = 0 +for char_s, char_t in zip(s, t): +    if char_s != char_t: +        ans += 1 +print(ans)