import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Map.Entry;
import java.util.Scanner;
import java.util.Set;

public class text1065true {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		HashMap<Integer, Integer> couple = new HashMap<>();
		int n = in.nextInt();
		while (n-- > 0) {
			int key = in.nextInt();
			int value = in.nextInt();
			couple.put(key, value);
		}
		Set<Entry<Integer, Integer>> s = couple.entrySet();
		ArrayList<Integer> alone = new ArrayList<>();
		ArrayList<Integer> test = new ArrayList<>();
		n = in.nextInt();
		while (n-- > 0) {
			test.add(in.nextInt());
		}
		for (int i = 0; i < test.size(); i++) {
			int a = test.get(i);
			boolean boy = couple.containsKey(a);
			boolean girl = couple.containsValue(a);
			boolean flag = false;
			Integer wife = 0;
			if (boy) {
				for (Entry<Integer, Integer> vo : couple.entrySet()) {
					if (vo.getKey() == a) {
						wife = vo.getValue();
						break;
					}
				}

				if (test.contains(wife)) {
					flag = true;
				}
			}
			if (girl) {
				for (Entry<Integer, Integer> vo : couple.entrySet()) {
					if (vo.getValue() == a) {
						wife = vo.getKey();
						break;
					}
				}

				if (test.contains(wife)) {
					flag = true;
				}
			}

			if (!flag) {
				alone.add(a);
			}
		}

		Object er[] = alone.toArray();
		Arrays.sort(er);
		System.out.println(er.length);
		for (int i = 0; i < er.length - 1; i++) {
			System.out.print(er[i] + " ");
		}
		System.out.print(er[er.length - 1]);
	}
}