class SLLNode<E>
{
    E element;
    SLLNode<E> succ;

    public SLLNode(E element, SLLNode<E> succ) {
        this.element = element;
        this.succ = succ;
    }
}
class SLL<E>
{
    SLLNode<E> first;

    public SLL()
    {
        first = null;
    }
    public void insertFirst(E element)
    {
        SLLNode<E> nov = new SLLNode(element,first);
        first = nov;
    }
    public void insertLast(E element)
    {
        if(first==null)
        {
            insertFirst(element);
        }
        else
        {
            SLLNode<E> nov = new SLLNode(element,null);
            SLLNode<E> dvizi = first;
            while(dvizi.succ!=null)
            {
                dvizi = dvizi.succ;
            }
            dvizi.succ = nov;
        }
    }
    @Override
    public String toString()
    {
        String s = new String();
        SLLNode<E> dvizi = first;
        while(dvizi!=null)
        {
            s = s + dvizi.element + " ";
            dvizi = dvizi.succ;
        }


        return s;
    }
}
public class Test
{
    public static void main(String[] args) {
        /*SLLNode<Integer> jazol1 = new SLLNode(5,null);
        SLLNode<String> jazol2 = new SLLNode("Dragan",null);
        SLLNode<Integer> jazol3 = new SLLNode(32,jazol1);*/

        SLL<Integer> lista = new SLL();
        lista.insertFirst(21);
        lista.insertFirst(1);
        lista.insertLast(4);
        lista.insertLast(12);


        System.out.println(lista);

    }
}