How do I access the :id parameter in the route file in ember.js?

I have these routes in my Ember app:

Router.map(function() {
  this.resource('posts', function () {
    this.route('show',  {path: '/:id'});
  });
});

Let's focus on the show route with url /posts/:id It uses the PostsShowController which looks like this:

import Ember from "ember";
export default Ember.ObjectController.extend({});

And the route file /routes/posts/show.js which looks like this:

import Ember from 'ember';

var PostsIndexRoute = Ember.Route.extend({
  model: function() {
    return posts[variable];
  }
});

var posts = ...

On the fifth line, where it says posts[variable] I want to replace variable with the :id parameter that gets passed in the url. So if I enter localhost:4200/posts/3 I want it to be 3. How do I do this?

Please be helpful rather than downvote and not even leave a comment. It's my first day using Ember