class IntSet18
{
// Constructive Set class, sets stored as ordered trees

 private Cell tree;

 public IntSet18()
 {
  tree=null;
 }

 private IntSet18(Cell t)
 {
  tree=t;
 }

 public IntSet18 delete(int n)
 {
  return new IntSet18(delete(n,tree));
 }

 private static Cell delete(int n,Cell t)
 {
  if(t==null)
     return null;
  else if(n<t.item)
     return new Cell(t.item,delete(n,t.left),t.right);
  else if(n>t.item)
     return new Cell(t.item,t.left,delete(n,t.right));
  else if(t.left==null)
     return t.right;
  else if(t.right==null)
     return t.left;
  else
     {
      int m=rightmost(t.left);
      Cell newleft=removeRightmost(t.left);
      return new Cell(m,newleft,t.right);
     }
 }

 private static int rightmost(Cell t)
 {
  if(t.right==null)
     return t.item;
  else
     return rightmost(t.right);
 }

 private static Cell removeRightmost(Cell t)
 {
  if(t.right==null)
     return t.left;
  else
     return new Cell(t.item,t.left,removeRightmost(t.right));
 }

 public IntSet18 add(int n)
 {
  return new IntSet18(add(n,tree));
 }

 private static Cell add(int n,Cell t)
 {
  if(t==null)
     return new Cell(n,null,null);
  else if(n==t.item)
     return t;
  else if(n<t.item)
     return new Cell(t.item,add(n,t.left),t.right);
  else
     return new Cell(t.item,t.left,add(n,t.right));
 }

 public boolean member(int n)
 {
  return member(n,tree);
 }

 private static boolean member(int n,Cell t)
 {
  if(t==null)
     return false;
  else if(t.item==n)
     return true;
  else if(n<t.item)
     return member(n,t.left);
  else
     return member(n,t.right);
 }

 public String toString()
 {
  return "{"+toString(tree)+"}";
 }

 public String treeString()
 {
  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 String toString(Cell tree)
 {
  if(tree==null)
     return "";
  else if(tree.left==null&&tree.right==null)
     return ""+tree.item;
  else if(tree.left==null)
     return tree.item+","+toString(tree.right);
  else if(tree.right==null)
     return toString(tree.left)+","+tree.item;
  else
     return toString(tree.left)+","+tree.item+","+toString(tree.right);
 }

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