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 java.util.function.*;
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 java.awt.geom.*;
import javax.imageio.*;
import java.math.*;
import java.time.Duration;
import java.lang.invoke.VarHandle;
import java.lang.invoke.MethodHandles;

class main {




// assumes that each set function is called only once
static class PairCollector<A, B> {
  volatile A a;
  volatile B b;
  volatile int counter;
  
  // statically get var handles
  private static final VarHandle vhA, vhB, vhCounter;
  static { try {
    var l = MethodHandles.lookup();
    vhA = l.findVarHandle(PairCollector.class, "a", Object.class);
    vhB = l.findVarHandle(PairCollector.class, "b", Object.class);
    vhCounter = l.findVarHandle(PairCollector.class, "counter", int.class);
  } catch (Exception __e) { throw rethrow(__e); } }
  
  void setA(A a) { this.a = a; incCounter(); }
  void setB(B b) { this.b = b; incCounter(); }
  
  IVF1<A> setterForA() { return a -> setA(a); }
  IVF1<B> setterForB() { return b -> setB(b); }
  
  private void incCounter() {
    if (((int) vhCounter.getAndAdd(this, 1))+1 == 2)
      complete(a, b);
  }
  
  // can override or swap
  transient  IVF2<A, B> complete;
void complete(A a, B b) { if (complete != null) complete.get(a, b); else complete_base(a, b); }
final void complete_fallback(IVF2<A, B> _f, A a, B b) { if (_f != null) _f.get(a, b); else complete_base(a, b); }
void complete_base(A a, B b) {}
}
static RuntimeException rethrow(Throwable t) {
  
  if (t instanceof Error)
    _handleError((Error) t);
  
  throw t instanceof RuntimeException ? (RuntimeException) t : new RuntimeException(t);
}

static RuntimeException rethrow(String msg, Throwable t) {
  throw new RuntimeException(msg, t);
}




static void _handleError(Error e) {
  //call(javax(), '_handleError, e);
}




static interface IVF1<A> {
  void get(A a);
}
static interface IVF2<A, B> {
  void get(A a, B b);
}

}