program minor_change
  implicit none
  character(200000) :: s, t
  integer :: n, i, x = 0
  read(*,*) s
  read(*,*) t
  n = len_trim(s)
  do i = 1, n
    if (s(i:i) /= t(i:i)) x = x + 1
  end do
  write(*,'(i0)') x
end program minor_change