#include <iostream>
#include <vector>
using namespace std;


#ifndef _STACK_H_
#define _STACK_H_

template<typename T>
class Stack : private vector<T> {
    public:
    	Stack() : vector<T>() {};
    	int size();
	using vector<T>::push_back;
};

#endif

template<typename T>
int Stack<T>::size() {
    return -1;
}

int main() {
    Stack<int> s;
    cout << s.size();
    cout << s.push_back(9);
    
    return 0;
}