Router

Hello everybody.
I want to replace CI 2.1 to CI 3.1
But i have a problem. I can't transfer to the function an argument from router.

Router:

PHP Code:

$route['default_controller'] = 'pages/show/ukr'; 


"ukr" - i can't transfer to the function in the class.!?
Class:

PHP Code:

class Pages extends CI_Controller{
    
    public function __construct(){
      parent::__construct();
      $this->load->model('pages_model');
    }
    
    public function show($page_id){   
      $data=array();
      $data['main_info']=$this->pages_model->get($page_id);
        $name='pages/mainpage';
        $this->display_lib->user_page($data,$name);                          
    }
} 


What is it.!?
This is as it should be?