import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        int m = sc.nextInt();
        int k = sc.nextInt();
        HashMap<Integer, HashMap<Integer, ArrayList<Integer>>> route = new HashMap<>();
        for (int i = 0; i < m; i++) {
            int a = sc.nextInt();
            int b = sc.nextInt();
            int c = sc.nextInt();
            if (!route.containsKey(c)) {
                route.put(c, new HashMap<>());
            }
            if (!route.get(c).containsKey(a)) {
                route.get(c).put(a, new ArrayList<>());
            }
            route.get(c).get(a).add(b);
            if (!route.get(c).containsKey(b)) {
                route.get(c).put(b, new ArrayList<>());
            }
            route.get(c).get(b).add(a);
        }
        ArrayList<TreeSet<Integer>> currents = new ArrayList<>();
        for (int i = 0; i <= k; i++) {
            currents.add(new TreeSet<>());
        }
        for (int i = 1; i <= n; i++) {
            currents.get(0).add(i);
        }
        for (int i = 0; i < k; i++) {
            int x = sc.nextInt();
            HashMap<Integer, ArrayList<Integer>> tmp = route.get(x);
            if (tmp == null) {
                break;
            }
            for (int y : currents.get(i)) {
                if (tmp.containsKey(y)) {
                    currents.get(i + 1).addAll(tmp.get(y));
                }
            }
        }
        StringBuilder sb = new StringBuilder();
        sb.append(currents.get(k).size()).append("\n");
        boolean isFirst = true;
        for (int x : currents.get(k)) {
            if (isFirst) {
                isFirst = false;
            } else {
                sb.append(" ");
            }
            sb.append(x);
        }
        System.out.println(sb);
    }
}