Baekjoon #10828

#include<bits/stdc++.h>

using namespace std;

int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);

    int N; cin >> N;

    stack<int> st;

    for(int i=0;i<N;i++){
        string cmd; cin >> cmd;
        if(cmd == "push") { 
            int X; cin >> X;
            st.push(X);
        }
        else if(cmd == "pop") {
            if(st.empty()) { 
                cout << -1 << '\n';
            }
            else {
                cout << st.top() << '\n';
                st.pop();
            }
        }
        else if(cmd == "size") {
            cout << (int)st.size() << '\n';
        }
        else if(cmd == "empty") {
            cout << st.empty() << '\n';
        }
        else if(cmd == "top") {
            if(st.empty()) {
                cout << -1 << '\n';
            }
            else {
                cout << st.top() << '\n';
            }
        }
    }
}

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

public class Main{
    static public void main(String[] args) {
        FastReader rd = new FastReader();

        int N = rd.nextInt();
        
        Stack<String> stack = new Stack<>(); 

        StringBuilder out = new StringBuilder();
        for(int i=0;i<N;i++){
            String[] Line = rd.nextLine().split(" ");
            String cmd = Line[0]; 

            if(cmd.equals("push")) {
                stack.push(Line[1]);
            }
            else if(cmd.equals("pop")) {
                if(stack.empty()){
                    out.append("-1");
                }
                else {
                    out.append(stack.peek());
                    stack.pop();
                }
                out.append("\n");
            }
            else if(cmd.equals("size")) {
                out.append(stack.size() + "\n");
            }
            else if(cmd.equals("empty")) {
                out.append(stack.empty() ? "1" : "0");
                out.append("\n");
            }
            else if(cmd.equals("top")) {
                if(stack.empty()){
                    out.append("-1\n");
                }
                else {
                    out.append(stack.peek() + "\n");
                }
            }
        }
        System.out.print(out);
    }

    static class FastReader {
        BufferedReader br;
        StringTokenizer st;

        public FastReader() {
            br = new BufferedReader(new InputStreamReader(System.in));
        }

        String next() {
            while(st == null || !st.hasMoreElements()) {
                try {
                    st = new StringTokenizer(br.readLine());
                }
                catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() { return Integer.parseInt(next()); }
        long nextLong() { return Long.parseLong(next()); }
        double nextDouble() { return Double.parseDouble(next()); }
        String nextLine() {
            String str = "";
            try {
                str = br.readLine();
            }
            catch (IOException e) {
                e.printStackTrace();
            }
            return str;
        }
    }
}

import sys

def input():
    return sys.stdin.readline().rstrip()

N = int(input())

stack = [] 

for i in range(N):
    cmd = input().split()
    X = 0
    if len(cmd) == 2:
        X = cmd[1]
    cmd = cmd[0]

    if cmd == "push":
        stack.append(X)
    elif cmd == "pop":
        if len(stack) == 0:
            print(-1)
        else:
            print(stack[-1])
            stack.pop(-1)
    elif cmd == "size":
        print(len(stack))
    elif cmd == "empty":
        print(0 if len(stack) else 1)
    elif cmd == "top":
        if len(stack) == 0:
            print(-1)
        else:
            print(stack[-1])