import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int N = Integer.parseInt(br.readLine());

        ArrayList<Integer> stack = new ArrayList<>();

        for (int i = 0; i < N; i++) {
            String command = br.readLine();

            // [1] push
            if (command.startsWith("push")) {
                int X = Integer.parseInt(command.split(" ")[1]);
                stack.add(X);

            // [2] pop
            } else if (command.equals("pop")) {
                if (!stack.isEmpty()) {
                    System.out.println(stack.get(stack.size() - 1));
                    stack.remove(stack.size() - 1);
                } else {
                    System.out.println(-1);
                }

            // [3] size
            } else if (command.equals("size")) {
                System.out.println(stack.size());

            // [4] empty
            } else if (command.equals("empty")) {
                System.out.println(stack.isEmpty() ? 1 : 0);

            // [5] top
            } else if (command.equals("top")) {
                if (!stack.isEmpty()) {
                    System.out.println(stack.get(stack.size() - 1));
                } else {
                    System.out.println(-1);
                }
            }
        }
    }
}