import java.util.Arrays;
import java.util.Scanner;

public class Yuki092 {
    public static void main(String[] args) {
        Yuki092 hoge = new Yuki092();
    }

    Yuki092() {
        Scanner scanner = new Scanner(System.in);
        int N = scanner.nextInt();
        int M = scanner.nextInt();
        int K = scanner.nextInt();

        int[] a = new int[M];
        int[] b = new int[M];
        int[] c = new int[M];


        boolean[] prev = new boolean[N + 1];

        Arrays.fill(prev, true);

        for (int i = 0; i < M; i++) {

            a[i] = scanner.nextInt();
            b[i] = scanner.nextInt();
            c[i] = scanner.nextInt();
        }
        for (int i = 0; i < K; i++) {
            int d = scanner.nextInt();

            boolean[] next = new boolean[1001];
            for (int j = 0; j < M; j++) {
                if (c[j] == d) {
                    int u = a[j], v = b[j];
                    if (prev[u]) {
                        next[v] = true;
                    }
                    if (prev[v]) {
                        next[u] = true;
                    }
                }
            }
            prev = next;
        }
        int count = 0;
        for (int j = 0; j < N; j++) {
            if (prev[j]) {
                count++;
            }
        }
        System.out.println(count);

        StringBuilder ans = new StringBuilder();
        for (int j = 0; j < N; j++) {
            if (prev[j]) {
                if (ans.length() > 0) {
                    ans.append(" ");
                }
                ans.append(j);
            }
        }
        System.out.println(ans);

    }

}