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

Create file MY_Router.php in application/core directory with code:

PHP Code:

<?php
class MY_Router extends CI_Router {

protected function _validate_request($segments)
 {
 $c = count($segments);
 $directory_override = isset($this->directory);

 // Loop through our segments and return as soon as a controller
 // is found or when such a directory doesn't exist
 while ($c-- > 0)
 {
 $test = $this->directory
 .ucfirst($this->translate_uri_dashes === TRUE ? str_replace('-', '_', $segments[0]) : $segments[0]);

 if ( ! file_exists(APPPATH.'controllers/'.$test.'.php')
 && $directory_override === FALSE
 && is_dir(APPPATH.'controllers/'.$this->directory.$segments[0])
 )
 {
 $this->set_directory(array_shift($segments), TRUE);
                while(count($segments) > 0 && is_dir(APPPATH.'controllers/'.$this->directory.$segments[0]))
                {
                    $this->set_directory($this->directory . $segments[0]);
                    $segments = array_slice($segments, 1);
                }
 continue;
 }

 return $segments;
 }

 // This means that all segments were actually directories
 return $segments;
 }
}