#include<iostream>
#define STACK_OVERFLOW 404
#define STACK_UNDERFLOW 401

using namespace std;

const int max = 20;

struct Stack
{
	int mas[max];
	int size;
};

void push(Stack& stack, int value)
{
	if (stack.size >= max)
	{
		exit(STACK_OVERFLOW);
	}
	stack.mas[stack.size] = value;
	stack.size++;
}
int pop(Stack& stack)
{
	if (stack.size == 0)
	{
		exit(STACK_UNDERFLOW);
	}
	stack.mas[stack.size - 1];
	stack.size--;
}

void print(Stack& stack)
{
	for (int i = 0; i < stack.size; i++)
	{
		cout << stack.mas[i] << " ";
	}
	cout << endl;

}

int main()
{


	Stack s;
	s.size = 0;

	push(s, 5);
	push(s, -3);
	push(s, 23);
	push(s, 12);
	print(s);

	pop(s);
	print(s);

	pop(s);
	print(s);

	pop(s);
	print(s);

	cin.ignore(2, '\n');
	return 0;
}