Wordpress, excude some pages from search

functions.php

/* Exclude some pages from search */
function gp_search_filter( $query ) {
  if ( ! $query->is_admin && $query->is_search && $query->is_main_query() ) {
    $query->set( 'post__not_in', array( 39,41 ) ); // add page ID's
  }
}

add_action( 'pre_get_posts', 'gp_search_filter' );