def main():

    s = eval(input())

    t = eval(input())

    r = 0

    for i, se in enumerate(s):

        if se != t[i]:

            r += 1

    print(r)



if __name__ == '__main__':

    main()

import sys

read = sys.stdin.read

readlines = sys.stdin.readlines

def main():

    s = eval(input())

    t = eval(input())

    r = 0

    for se, te in zip(s, t):

        r += se != te

    print(r)





if __name__ == '__main__':

    main()
def main():
    s = eval(input())
    t = eval(input())
    r = 0
    for i, se in enumerate(s):
        if se != t[i]:
            r += 1
    print(r)


if __name__ == "__main__":
    main()

import sys

read = sys.stdin.read
readlines = sys.stdin.readlines


def main():
    s = eval(input())
    t = eval(input())
    r = 0
    for se, te in zip(s, t):
        r += se != te
    print(r)


if __name__ == "__main__":
    main()

+import sys + +read = sys.stdin.read +readlines = sys.stdin.readlines + + -    for i, se in enumerate(s): -        if se != t[i]: -            r += 1 +    for se, te in zip(s, t): +        r += se != te