Show posts by logged in user and admin in the backend dashboard

I have users (contributors) who log into my WordPress backend admin to submit their posts. I don’t want users seeing other users’ posts. When a user logs in, he should just see his own posts in the backend admin area; in addition, I want the logged in user to see posts by the admin (user # 1).

This is the working code I have in my functions.php file to display posts written by the logged in user in the backend:

function posts_for_current_author($query) {
	global $user_level;

	if($query->is_admin && $user_level < 5) {
		global $user_ID;
		$query->set('author',  $user_ID);

		unset($user_ID);

	}
	unset($user_level);
	unset($user_ID);

	return $query;
}
add_filter('pre_get_posts', 'posts_for_current_author');

My problem is this code only shows posts written by the logged in user; I want the user also to see posts written by the admin. How do I do it?

Thank you,
Brian