import sys

read = sys.stdin.buffer.read

readline = sys.stdin.buffer.readline

S,T=read().rstrip().decode().split()

ans=0

for s,t in zip(S,T):

    if s!=t:

        ans+=1

print(ans)
import sys

read = sys.stdin.buffer.read

readline = sys.stdin.buffer.readline

S,T=read().rstrip().decode().split()

print((sum(s!=t for s,t in zip(S,T))))
import sys

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
S, T = read().rstrip().decode().split()
ans = 0
for s, t in zip(S, T):
    if s != t:
        ans += 1
print(ans)

import sys

read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
S, T = read().rstrip().decode().split()
print((sum(s != t for s, t in zip(S, T))))

-ans = 0 -for s, t in zip(S, T): -    if s != t: -        ans += 1 -print(ans) +print((sum(s != t for s, t in zip(S, T))))