[백준] 28278번 스택 2

import java.util.Scanner;
import java.util.Stack;

public class Main {
	public static void main(String[] args) {
		
		Stack<Integer> stack = new Stack<>();
		
		Scanner kb = new Scanner(System.in);
		StringBuilder sb = new StringBuilder();
		
		int N = kb.nextInt();
		
		for(int i=0; i<N; i++) {
			
			int order = kb.nextInt();
			
			switch(order) {
			case 1:
				stack.push(kb.nextInt());
				break;
			
			case 2:
				if(stack.isEmpty()) {
					sb.append(-1).append('\n');
				}else {
					sb.append(stack.pop()).append('\n');
					
				}
				break;
				
			case 3:
				sb.append(stack.size()).append('\n');
				break;
				
			case 4: 
				if(stack.isEmpty()) {
					sb.append(1).append('\n');
				}else {
					sb.append(0).append('\n');
					
				}
				break;
				
				
			case 5: 
				if(stack.isEmpty()) {
					sb.append(-1).append('\n');
				}else {
					sb.append(stack.peek()).append('\n');
					
				}
				break;
			}

		}
		
		System.out.println(sb.toString());
		
		
	}
}