How to identify Routing rule that used that directed to my Codeigniter controller?

Question

In my Application
I have 3 routing rules (defined in routes.php file) thats directed to the one controller

$route[urlencode('news')]       = "news/show-news";  
$route[urlencode('letters')]    = "news/show-news";  
$route[urlencode('papers')]     = "news/show-news"; 

so
if any user navigate to any of those URLs
http://example.com/news/
http://example.com/letters/
http://example.com/papers/

The target controller will be news/show-news

My need
How to identify Routing rule that used that directed to my Codeigniter controller?

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');
class News extends CI_Controller {
    public function show-news(){        
        // came from [news OR letters OR papers]  ??

    }   
}

Answer 1

First thanks to @aspirinemaga
His answer is correct
But if we want to do that without using parametric controller function
We can do that

public function show-news(){

    // came from [news OR letters OR papers]  ??
    $requested_URI_segment = $this->uri->segment(1);
    $requested_URI_segment = urldecode($requested_URI_segment);

    switch ( $requested_URI_segment ){
        // If news requested
        case 'news':
            // your code here
            echo 'news requested'. '</br>';
        break;

        // If letters requested
        case 'letters':
            // your code here
            echo 'letters requested'. '</br>';
        break;

        // If papers requested
        case 'papers':
            // your code here
            echo 'papers requested'. '</br>';
        break;

        // Default landing if nothing provided
        default:
            // your code here
            echo 'select one of the show method'. '</br>';

    }