import java.util.*;

class Tree
{
 private Cell tree;

 public static Tree empty()
 {
  return new Tree(null);
 }

 private Tree(Cell l)
 {
  tree=l;
 }

 public int item()
 {
  return tree.item;
 }

 public Tree left()
 {
  return new Tree(tree.left);
 }

 public Tree right()
 {
  return new Tree(tree.right);
 }

 public static Tree make(int n,Tree l,Tree r)
 {
  return new Tree(new Cell(n, l.tree,r.tree));
 }

 public boolean isEmpty()
 {
  return tree==null;
 }

 public String toString()
 {
  return treeString("",tree);
 }

 private static String treeString(String indent,Cell tree)
 {
  if(tree==null)
     return "\n";
  else if(tree.left==null&&tree.right==null)
     return indent+tree.item+"\n";
  else
    return treeString(indent+"     ",tree.right)+
           indent+tree.item+"\n"+
           treeString(indent+"     ",tree.left);
 }
 
 private static class Cell
 {
  int item;
  Cell left,right;

  Cell(int n,Cell l,Cell r)
  {
   item=n;
   left=l;
   right=r;
  }
 }
}