program main
  implicit none
  integer(8) i, n, ans
  character(2*10**5) S, T
  read(*, *) S
  read(*, *) T
  !read(*, *) (L(i), i = 1,N)
  n = len(trim(S))
  ans = n
  do i = 1, n
    if (S(i:i) == T(i:i)) then
      ans = ans-1
    endif
  enddo
  write(*, *) ans
end program main
