if(!function_exists('get_post_top_ancestor_id')){
/**
 * Gets the id of the topmost ancestor of the current page. Returns the current
 * page's id if there is no parent.
 *
 * @uses object $post
 * @return int
 */
function get_post_top_ancestor_id(){
    global $post;

    if($post->post_parent){
        $ancestors = array_reverse(get_post_ancestors($post->ID));
        return $ancestors[0];
    }

    return $post->ID;
}}