program sample
implicit none

character(len=2*10**5) :: S, T
integer :: a, i, sum, ans
character(1), allocatable :: p(:), q(:)

read(*,*) S, T
a = len_trim(S)
allocate(p(a))
allocate(q(a))

do i = 1, a
p(i)=S(i:i)
enddo

do i = 1, a
q(i)=T(i:i)
enddo

sum=0
do i =1, a
if(p(i) == q(i))then
sum = sum+1
endif
enddo 
ans = a - sum
write(*,*) ans

deallocate(p)
deallocate(q)

stop
end program sample