import java.util.*;

public class LinkedList {
// instance variables
   private Node head, tail;
   private int size;

// methods
   public LinkedList() {
     head = tail = null; size = 0; 
   }

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

   public void addHead(Object d) {
     Node n = new Node(d, head);
     head = n;
     size++;
     if (tail == null) tail = head;
   }

   public void addTail(Object d) {
     Node n = new Node(d, null);
     if (tail == null) head = tail = n;
     else {
        tail.setNext(n);
        tail = n;
     }
     size++;
   }

   public Object removeHead() {
     if (head == null) throw new RuntimeException("Empty List");
     Node n = head;
     head = head.getNext();
     if (head == null) tail = head;
     size--;
     return n.getData();
   }
 
// LinkedList testing methods:
   public String toString() {
      String ans = "";
      Node n = head;
      ans += "(H)-->";
      while (n != null) {
        ans += n.getData();
        ans += "-->";
        n = n.getNext();
      }
      return ans + "(T)";
   }

   public static void main(String args[]) {
      LinkedList l = new LinkedList();
      try {
        Scanner s = new Scanner(System.in); 
        while (true) {
           System.out.println( l + "  :cmds are H T R Q: ");
           String cmd = s.next();
           if (cmd.charAt(0) == 'Q') throw new Exception();
           if (cmd.charAt(0) == 'R') l.removeHead();
           else {
              String entry = s.next();
              if (cmd.charAt(0) == 'H') l.addHead(entry);
              if (cmd.charAt(0) == 'T') l.addTail(entry);
           }
        }   
      } catch (Exception e) { }
   }
}