program main
    use,intrinsic :: iso_fortran_env
    implicit none
    integer(int32):: ls, i, cnt=0
    character(200000):: s,t

    read*, s
    read*, t

    do i=1,len_trim(s)
        if (s(i:i) /= t(i:i)) cnt=cnt+1
    end do
    print'(i0)', cnt
end program main