Node<E> succ() { /* kod */
        if (right == null) {
            if (parent == null) return null;
            if (parent.left == this) {
                return parent;
            } else {
                return parent.succNoRight();
            }
        } else {
            Node<E> current = right;
            while (true) {
                if (current.left != null) {
                    current = current.left;
                } else {
                    return current;
                }
            }
        }
    }

    private Node<E> succNoRight() {
        if (parent == null) return null;
        if (parent.left == this) {
            return parent;
        } else {
            return parent.succNoRight();
        }
    }