import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Collections;

public class No92 {

	public static void main(String[] args) throws IOException {
		
		String[] strings = readStr();
		
		int n = Integer.parseInt(strings[0].split(" ")[0]);
		int m = Integer.parseInt(strings[0].split(" ")[1]);
		int k = Integer.parseInt(strings[0].split(" ")[2]);
		
		int[][] c = new int[m][3];
		String[] str;
		int a , b, c2;
		
		for(int i = 1;i <= m;i++) {
			str = strings[i].split(" ");
			a = Integer.parseInt(str[0]);
			b = Integer.parseInt(str[1]);
			c2 = Integer.parseInt(str[2]);
			
			c[i-1][0] = a;
			c[i-1][1] = b;
			c[i-1][2] = c2;
		}
		
		int d = 0;
		ArrayList<Integer> placeB = new ArrayList<Integer>();
		ArrayList<Integer> placeA = new ArrayList<Integer>();
		for(int i = 0;i < k;i++) {
			d = Integer.parseInt(strings[m+1].split(" ")[i]);
			
			for(int[] abc : c) {
				
				if(abc[2] == d) {
					
					if(i == 0) {
						placeA.add(abc[0]);
						placeA.add(abc[1]);
						continue;
					}
					
					if(placeB.contains(abc[0]) && !placeA.contains(abc[1])) {
						placeA.add(abc[1]);
					}
					if(placeB.contains(abc[1]) && !placeA.contains(abc[0])) {
						placeA.add(abc[0]);
					}
				}
			}
			
			placeB = placeA;
			placeA = new ArrayList<Integer>();
			
		}
		
		System.out.println(placeB.size());
		Collections.sort(placeB);
		for(int p :placeB) {
			System.out.print(p + " ");
		}
		System.out.println();
		
		
		
	}
	
	public static String[] readStr() throws IOException{
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		ArrayList<String> list = new ArrayList<>();

		do {
			list.add(br.readLine());
		}while(br.ready());

		br.close();

		String[] text = new String[list.size()];
		list.toArray(text);

		return text;

	}

}