import java.util.ArrayList;
import java.util.List;

public class MyClass  {
    private static int numberOfInstance = 0;
    private static List<MyClass> instances = new ArrayList<>();
    private static MyClass prev = null;
    private static int prevX = -1;
    private int x;
    private MyClass (int x) {
        this.x = x;
        numberOfInstance++;
        instances.add(this);
    }

    public static MyClass instance (int x) {
        if (++numberOfInstance % 2 == 0) {
            prev = new MyClass(prevX);
            return new MyClass(x);
        }
        for (int i = 0; i < instances.size(); i++) {
            instances.set(i, null);
        }
        prev = null;
        return null;
    }


    public int getX () {
        return x;
    }
}