using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp2
{
    class Program
    {
        static void Main(string[] args)
        {
            Stack stk = new Stack(100);

            int rounds = Convert.ToInt32(Console.ReadLine());

            for (int i = 1; i <= rounds; i++)
            {
                string[] str = Console.ReadLine().Split(' ');
                switch (str[0])
                {
                    case "push":
                        stk.push(Convert.ToInt32(str[1]));
                        Console.WriteLine("stack pushed key : " + str[1]);
                        break;
                    case "pop":
                        if (!stk.IsEmpty())
                        {
                            Console.WriteLine(stk.pop());
                        }
                        else
                        {
                            Console.WriteLine("-1");
                        }

                        break;
                    case "size":
                        Console.WriteLine(stk.Size());
                        break;
                    case "top":

                        if (!stk.IsEmpty())
                        {
                            Console.WriteLine(stk.peek());
                        }
                        else
                        {
                            Console.WriteLine("-1");
                        }

                        break;
                    case "empty":

                        if (!stk.IsEmpty())
                        {
                            Console.WriteLine("0");
                        }
                        else
                        {
                            Console.WriteLine("1");
                        }

                        break;
                }
            }
        }
    }

    class Stack
    {
        int top, size;
        int[] stack;

        public Stack(int size)
        {
            top = 0;
            stack = new int[size];
            this.size = size;
        }

        public int peek()
        {
            return stack[top];
        }

        public void push(int value)
        {
            stack[++top] = value;
        }

        public int pop()
        {
            return stack[top--];
        }

        public bool IsEmpty()
        {
            if(top > 0)
            {
                return false;
            }
            else
            {
                return true;
            }
        }

        public int Size()
        {
            return top;
        }

    }
}