SoftUni Party

package SetsAndMaps;

import java.util.Scanner;
import java.util.TreeSet;

public class SoftUniParty {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        TreeSet<String> guestId = new TreeSet<>();
        String command;

        while (!"PARTY".equals(command = scanner.nextLine())) {
            guestId.add(command);
        }

        while (!"END".equals(command = scanner.nextLine())) {
            guestId.remove(command);
        }
        System.out.println(guestId.size());

        for (String people : guestId) {
            System.out.println(people);
        }
    }
}