Delete post media except featured image

If someone has clashed with such problem, I solved it in this way:

$attachments = get_posts( array(
    'post_type'      => 'attachment',
    'posts_per_page' => -1,
    'post_status'    => 'any',
    'post_parent'    => $post_id
) );
$thumbId = get_post_thumbnail_id($post_id);
foreach ( $attachments as $attachment ) {
    if($thumbId != $attachment->ID) wp_delete_attachment( $attachment->ID, true );
}