import java.util.*;

// doubly linked list, uses header and trailer sentinels.

public class DList {
   private DNode header, trailer;
   private int size;

   public DList() {
     size = 0; 
     header = new DNode(null, null, null);
     trailer = new DNode(null, header , null);
     header.setNext(trailer);
   }

   public int size() {return size;}
   public boolean isEmpty() {return size == 0;}

   public DNode getFirst() {
     if (isEmpty()) throw new RuntimeException("Empty");
     return header.getNext();
   }
   public DNode getLast() {
     if (isEmpty()) throw new RuntimeException("Empty");
     return trailer.getPrev();
   }
   public DNode getNext(DNode v) {
     DNode ans = v.getNext();
     if (ans == null)
       throw new RuntimeException("No such node");
     return ans;
   }
   public DNode getPrev(DNode v) {
     DNode ans = v.getPrev();
     if (ans == null)
       throw new RuntimeException("No such node");
     return ans;
   }

   public void addBefore(Object d, DNode v) {
      DNode u = getPrev(v);   // throws if illegal
      DNode x = new DNode(d, u, v);
      u.setNext(x);
      v.setPrev(x);
      size ++;
   }
   public void addAfter(Object d, DNode v) {
      DNode w = getNext(v);   // throws if illegal
      DNode x = new DNode(d, v, w);
      v.setNext(x);
      w.setPrev(x);
      size ++;
   }
   public void addFirst(Object d) {
      addAfter(d, header);
   }
   public void addLast(Object d) {
      addBefore(d, trailer);
   }
   public Object remove(DNode v) {
      if (v == header || v == trailer) 
        throw new RuntimeException("Sentinel");
      DNode u = v.getPrev();
      DNode w = v.getNext();
      w.setPrev(u);
      u.setNext(w);
      size --;
      return v.getData();
   }
 
// LinkedList testing methods:
   public String toString() {
      String ans = "";
      DNode n = header;
      ans += "(H)<-->";
      do {
         n = n.getNext();
         if (n == trailer) ans += "(T)";
         else ans += (n.getData() + "<-->");
      } while (n != trailer);
      return ans;
   }

   public static void main(String args[]) {
      DList l = new DList();
      DNode d = null;
      boolean done = false;
      while (!done) {
         try {
           Scanner s = new Scanner(System.in);
           System.out.print( l + "  ");
           if (d != null && d.getData() != null) 
             System.out.print( " ^^ " + d.getData());
           System.out.println("\ncmds are F L B A R + - Q: >>");
           String cmd = s.next();
           String entry = null;
           char command = cmd.charAt(0);
           if (command == 'F' || command == 'L' ||
             command == 'B' || command == 'A') entry = s.next();
           switch (cmd.charAt(0)) {
              case 'Q': done = true; break; 
              case 'R': DNode e = d.getNext(); 
                        l.remove(d); d = e; break;
              case '+': d = l.getNext(d); break;
              case '-': d = l.getPrev(d); break;
              case 'F': l.addFirst(entry); d = l.getFirst(); break;
              case 'L': l.addLast(entry); d = l.getLast();break;
              case 'B': l.addBefore(entry, d); d = l.getPrev(d); break;
              case 'A': l.addAfter(entry, d); d = l.getNext(d); break;
           }
        } catch (Exception e) {
           System.out.println("Error " + e.toString());
        }
      }   
   }
}

class DNode {
   private Object data;
   private DNode prev, next;
   
   public DNode(Object d, DNode p, DNode n) {
     data = d; next = n; prev = p; }
   public Object getData() { return data; }
   public DNode getNext() { return next; }
   public DNode getPrev() { return prev; }
   public void setData(Object d) { data = d; }
   public void setNext(DNode n) { next = n; }
   public void setPrev(DNode p) { prev = p; }
}