interface MyIterator<T> {

    boolean hasNext();

    T next();
}

class MyLinkedList {

    private static class Node implements MyIterator<Node>{

        private int data;

        private Node next;

        public Node(int data) {
            this.data = data;
        }

        @Override
        public boolean hasNext() {
            return this.next != null;
        }

        @Override
        public Node next() {
            if(this.next == null) {
                throw new RuntimeException("no elements");
            }
            return this.next;
        }
    }

    private Node head = null;

    public void addAtFront(int element) {
        Node node = new Node(element);
        node.next = this.head;
        this.head = node;
    }

    public void addAtEnd(int element) {
        Node node = new Node(element);
        if (this.head == null) {
            this.head = node;
        } else {
            Node iterator = this.head;
            while (iterator.hasNext()) {
                iterator = iterator.next();
            }
            iterator.next = node;
        }
    }
}