Wordpress: Displaying Article Thumbnail of parent page on Child Page

hs_get_parent_post_thumbnail.php

<?php

global $post;

if ( is_page() ) { 

	/* Get an array of Ancestors and Parents if they exist */
	$parents = get_post_ancestors( $post->ID );

	/* Get the top Level page->ID count base 1, array base 0 so -1 */ 
	$id = ($parents) ? $parents[count($parents)-1]: $post->ID;

	echo get_the_post_thumbnail( $id, 'full' );

}

?>