import java.util.*;
import java.util.zip.*;
import java.util.List;
import java.util.regex.*;
import java.util.concurrent.*;
import java.util.concurrent.atomic.*;
import java.util.concurrent.locks.*;
import javax.swing.*;
import javax.swing.event.*;
import javax.swing.text.*;
import javax.swing.table.*;
import java.io.*;
import java.net.*;
import java.lang.reflect.*;
import java.lang.ref.*;
import java.lang.management.*;
import java.security.*;
import java.security.spec.*;
import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import javax.imageio.*;
import java.math.*;
class main {


static class Var<A> implements IVar<A> {
  Var() {}
  Var(A v) {
  this.v = v;}

  
  A v; // you can access this directly if you use one thread
  
  public synchronized void set(A a) {
    if (v != a) {
      v = a;
      notifyAll();
    }
  }
  
  public synchronized A get() { return v; }
  public synchronized boolean has() { return v != null; }
  public synchronized void clear() { v = null; }
  
  public String toString() { return str(this.get()); }
}

static interface IVar<A> extends IF0<A> {
  void set(A a);
  A get();
  
  default boolean has() { return get() != null; }
  default void clear() { set(null); }
  
}

static interface IF0<A> {
  A get();
}

static String str(Object o) {
  return o == null ? "null" : o.toString();
}

static String str(char[] c) {
  return new String(c);
}


}