백준 11279번(Java)

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

public class Main {

	public static void main(String[] args) throws IOException {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		
		int N = Integer.parseInt(br.readLine());
		
		PriorityQueue<Integer> queue = new PriorityQueue<>(Collections.reverseOrder());
		StringBuilder sb = new StringBuilder();
		
		for(int i=0; i<N; i++) {
			int num = Integer.parseInt(br.readLine());
			if(num == 0) {
				if(queue.isEmpty()) {
					sb.append(0).append('\n');
				} else {
					sb.append(queue.poll()).append('\n');
				}
			} else {
				queue.offer(num);
			}
		}
		System.out.println(sb);
	}
}