#include <iostream>
#include <vector>

template <class T>
class Singleton {
public:
  static T& GetInstance() {
    static T instance_;
    return instance_;
  }

protected:
  Singleton() {}
};

class Foo : public Singleton<Foo> {
public:
  std::vector<int> value;
};

int main() {
  Foo::GetInstance().value.push_back(1);
  std::cout << Foo::GetInstance().value.size() << "\n";
  std::cout << "Hello\n";
  return 0;
}