import java.util.Scanner;

// Create by Inho 2018. 3. 27. 오전 10:22:05

// 10828 스택

public class Study_10828 {

public static void main(String[] args) {

Scanner scanner = new Scanner(System.in);

int TC = scanner.nextInt();

scanner.nextLine();

int[] stack = new int[10000];

int state = 0;

while(TC--> 0){

String message = scanner.nextLine();

String[] tokens = message.split(" ");

switch(tokens[0]){

case "size":

System.out.println(state);

break;

case "pop":

if(state == 0){

System.out.println("-1");

break;

}

else{

state--;

System.out.println(stack[state]);

stack[state]=0;

break;

}

case "empty":

if(state ==0){

System.out.println("1");

break;

}

else{

System.out.println("0");

break;

}

case "top":

if(state == 0){

System.out.println("-1");

break;

}

else{

System.out.println(stack[state-1]);

break;

}

case "push":

int value = Integer.valueOf(tokens[1]);

stack[state] = value;

state++;

break;

}

}

}

}