program million_change
    character :: S(200001)
    character :: T(200001)
    integer i
    integer :: k = 0
    read *, S(200001)
    read *, T(200001)
    do i = 1, size(S)
        if(S(i) /= T(i))then
            S(i)  = T(i)
            k = k + 1
        end if
    end do
    print "('',i0)", k
end program