题解 | #【模板】栈#

import java.util.*;

// 注意类名必须为 Main, 不要有任何 package xxx 信息


public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        // 注意 hasNext 和 hasNextLine 的区别
        int n = in.nextInt();
        Stack<Integer> stack = new Stack<>();
        in.nextLine();
        for (int i = 0; i < n; i++) {
            String[] parts=in.nextLine().split(" ");
            String command = parts[0];

            switch (command) {
                case "push":
                    int x = Integer.parseInt(parts[1]);
                    stack.push(x);
                    break;
                case "pop":
                    if (!stack.isEmpty()) {
                        System.out.println(stack.pop());
                    }else{
                        System.out.println("error");
                    }
                    break;
                case "top":
                    if (!stack.isEmpty()) {
                        System.out.println(stack.peek());
                    }else{
                        System.out.println("error");
                    }
                    break;
            }
        }


    }
}