Codeigniter 3 controller in sub folder

In controller I have a folder named "landing".Inside this folder I have a controller name "Landingg.php"
code
------
<?php
defined('BASEPATH') OR exit('No direct script access allowed');
class Landingg extends CI_Controller {
    public function __construct() {
parent::__construct();
$this->load->helper('url');
    }

    public function index() {
echo 12;
    }

}

when I hit the url "http://localhost/ci/landing/landingg/" it shows object not found.Plz help how to implements and call controller with in sub folder in codeigniter 3