[APS] - Razigrana lista

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

class DLLNode<E> {
    protected E element;
    protected DLLNode<E> pred, succ;

    public DLLNode(E elem, DLLNode<E> pred, DLLNode<E> succ) {
        this.element = elem;
        this.pred = pred;
        this.succ = succ;
    }

    @Override
    public String toString() {
        return "<-"+element.toString()+"->";
    }
}


class DLL<E> {
    private DLLNode<E> first, last;

    public DLL() {
        // Construct an empty SLL
        this.first = null;
        this.last = null;
    }
    public void setFirst(DLLNode<E> pom) {
        first = pom;
    }
    public DLLNode<E> getFirst() {
        return first;
    }
    public void deleteList() {
        first = null;
        last = null;
    }

    public int length() {
        int ret;
        if (first != null) {
            DLLNode<E> tmp = first;
            ret = 1;
            while (tmp.succ != null) {
                tmp = tmp.succ;
                ret++;
            }
            return ret;
        } else
            return 0;

    }

    public void insertFirst(E o) {
        DLLNode<E> ins = new DLLNode<E>(o, null, first);
        if (first == null)
            last = ins;
        else
            first.pred = ins;
        first = ins;
    }

    public void insertLast(E o) {
        if (first == null)
            insertFirst(o);
        else {
            DLLNode<E> ins = new DLLNode<E>(o, last, null);
            last.succ = ins;
            last = ins;
        }
    }

    public void insertAfter(E o, DLLNode<E> after) {
        if(after==last) {
            insertLast(o);
            return;
        }
        DLLNode<E> ins = new DLLNode<E>(o, after, after.succ);
        after.succ.pred = ins;
        after.succ = ins;
    }

    public void insertBefore(E o, DLLNode<E> before) {
        if(before == first) {
            insertFirst(o);
            return;
        }
        DLLNode<E> ins = new DLLNode<E>(o, before.pred, before);
        before.pred.succ = ins;
        before.pred = ins;
    }

    public E deleteFirst() {
        if (first != null) {
            DLLNode<E> tmp = first;
            first = first.succ;
            if (first != null) first.pred = null;
            if (first == null)
                last = null;
            return tmp.element;
        } else
            return null;
    }

    public E deleteLast() {
        if (first != null) {
            if (first.succ == null)
                return deleteFirst();
            else {
                DLLNode<E> tmp = last;
                last = last.pred;
                last.succ = null;
                return tmp.element;
            }
        }
        // else throw Exception
        return null;
    }

public void setLast(DLLNode<E> node)
    {
        last = node;
    }
    @Override
    public String toString() {
        String s = new String();
        DLLNode<E> dvizi = first;
        while(dvizi!=null)
        {
            if(dvizi.succ==null)
                s = s+ dvizi.element;
            else
                s = s+ dvizi.element+" ";
            dvizi = dvizi.succ;
        }
        return s;
    }



    public DLLNode<E> getLast() {

        return last;
    }

}
public class Rt {

    public static String otstranuvanje(DLL<String> lista)
    {

        while(lista.getFirst().succ!=null)
        {
            DLLNode<String> dvizi = lista.getFirst().succ;
            while(dvizi!=null)
            {
                DLLNode<String> p1 = dvizi.pred;
                DLLNode<String> p2 = dvizi.succ;
                p1.succ = p2;
                if(p2!=null)
                {
                    p2.pred = p1;
                    dvizi = p2.succ;
                }
                else
                {
                   lista.setLast(p1);
                   dvizi =p2;
                }
            }
            System.out.println(lista);
            if(lista.getFirst().succ==null)
                break;
            dvizi = lista.getLast().pred;
            while(dvizi!=null)
            {
                DLLNode<String> p1 = dvizi.pred;
                DLLNode<String> p2 = dvizi.succ;
                p2.pred = p1;
                if(p1!=null)
                {
                    p1.succ = p2;
                    dvizi = p1.pred;
                }

                else
                {
                    lista.setFirst(p2);
                       dvizi = p1;
                }
            }
            System.out.println(lista);

        }
        return lista.getFirst().element;
    }
    public static void main(String[] args) throws IOException {
        DLL<String> lista = new DLL<>();
        BufferedReader stdin = new BufferedReader(new InputStreamReader(System.in));
        String s =stdin.readLine();
        String pomniza[] = s.split(" ");
        /*s.trim();
        char niza[] = s.toCharArray();*/

        for(int i=0;i<pomniza.length;i++)
        {
            lista.insertLast(pomniza[i]);
        }
        System.out.println(otstranuvanje(lista));
    }

}