import java.util.Iterator;

// Custom Linked List class using Generics
class List<T> implements Iterable<T> 
{
    Node<T> head, tail;

    // add new Element at tail of the linked list in O(1)
    public void add(T data)
    {
        Node<T> node = new Node<>(data, null);
        if (head == null)
            tail = head = node;
        else {
            tail.setNext(node);
            tail = node;
        }
    }

    // return Head
    public Node<T> getHead()
    {
        return head;
    }

    // return Tail
    public Node<T> getTail()
    {
        return tail;
    }

    // return Iterator instance
    public Iterator<T> iterator()
    {
        return new ListIterator<T>(this);
    }
}