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

const int MAX = 10000 + 1;

int idx;
int arr[MAX];

// stl 사용하지 않고 구현
int top(void)
{
	return arr[idx - 1];
}

void push(int num)
{
	arr[idx++] = num;
}

void pop(void)
{
	idx--;
}

int main(void)
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	int N;
	cin >> N;

	for (int n = 0; n < N; n++)
	{
		string s;
		cin >> s;

		if (s == "push")
		{
			int num;
			cin >> num;

			push(num);
		}
		else if (s == "pop")
		{
			if (idx)
			{
				cout << top() << "\n";
				pop();
			}
			else
				cout << -1 << "\n";
		}
		else if (s == "size")
		{
			cout << idx << "\n";
		}
		else if (s == "empty")
		{
			bool flag = (idx == 0);
			cout << flag << "\n";
		}
		else
		{
			if (idx)
				cout << top() << "\n";
			else
				cout << -1 << "\n";
		}
	}
	return 0;
}