[アルゴリズム]Baekjun-10828(スタック)/Java

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

class Main {
	public static void main(String args[]) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		int N = Integer.parseInt(br.readLine());
		StringTokenizer st;
		Stack<Integer> stack = new Stack<Integer>();
		StringBuilder sb = new StringBuilder();
		for (int i = 0; i < N; i++) {
			st = new StringTokenizer(br.readLine());
			String type = st.nextToken();
			switch (type) {
			case "push":

				stack.push(Integer.parseInt(st.nextToken()));
				break;
			case "pop":
				if (stack.isEmpty()) {
					sb.append("-1").append("\n");
					break;
				}
				sb.append(stack.pop()).append("\n");
				break;
			case "size":
				sb.append(stack.size()).append("\n");
				break;
			case "empty":
				sb.append(stack.isEmpty() ? 1 : 0).append("\n");
				break;
			case "top":
				if (stack.isEmpty()) {
					sb.append("-1").append("\n");
					break;
				}
				sb.append(stack.peek()).append("\n");
				break;
			}
		}
		System.out.print(sb);

	}
}