#include <iostream>

class Singleton 
{
public:
  static Singleton* Instance();
  static int get_number() { return number;}
  static void DelInstance();
protected:
  Singleton() {
    number ++;
  }
  ~Singleton() {
    number --;
  }
private:
  static Singleton* _instance;
  static int number;
};

int Singleton::number;

Singleton* Singleton::_instance = 0;
Singleton* Singleton::Instance () 
{
 if (_instance == 0) 
 _instance = new Singleton;
 return _instance;
}

void Singleton::DelInstance() {
  delete _instance;
  _instance = 0;
}

using namespace std;

int main() {
  cout << "number = " << Singleton::get_number() << endl;
  cout << "calling Instance" << endl;
  Singleton *sn = Singleton::Instance();
  cout << "number = " << Singleton::get_number() << endl;
  cout << "calling DelInstance" << endl;
  Singleton::DelInstance();
  cout << "number = " << Singleton::get_number() << endl;
  return 0;
}