import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.*;

public class Main {

    void solve() throws IOException {
        int n = ni(), m = ni(), k = ni();
        int[] a = new int[m];
        int[] b = new int[m];
        int[] c = new int[m];
        for (int i = 0; i < m; i++) {
            a[i] = ni() - 1;
            b[i] = ni() - 1;
            c[i] = ni();
        }
        int[] d = nia(k);

        boolean[] can = new boolean[n];
        Arrays.fill(can, true);
        for (int i = 0; i < k; i++) {
            boolean[] next = new boolean[n];
            for (int j = 0; j < m; j++) {
                if (c[j] == d[i]) {
                    if (can[a[j]]) next[b[j]] = true;
                    if (can[b[j]]) next[a[j]] = true;
                }
            }
            can = next;
        }

        ArrayList<Integer> ans = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            if (can[i]) ans.add(i + 1);
        }

        out.println(ans.size());
        for (int i = 0; i < ans.size(); i++) {
            if (i > 0) out.print(" ");
            out.print(ans.get(i));
        }
        out.println();
    }

    String ns() throws IOException {
        while (!tok.hasMoreTokens()) {
            tok = new StringTokenizer(in.readLine(), " ");
        }
        return tok.nextToken();
    }

    int ni() throws IOException {
        return Integer.parseInt(ns());
    }

    long nl() throws IOException {
        return Long.parseLong(ns());
    }

    double nd() throws IOException {
        return Double.parseDouble(ns());
    }

    String[] nsa(int n) throws IOException {
        String[] res = new String[n];
        for (int i = 0; i < n; i++) {
            res[i] = ns();
        }
        return res;
    }

    int[] nia(int n) throws IOException {
        int[] res = new int[n];
        for (int i = 0; i < n; i++) {
            res[i] = ni();
        }
        return res;
    }

    long[] nla(int n) throws IOException {
        long[] res = new long[n];
        for (int i = 0; i < n; i++) {
            res[i] = nl();
        }
        return res;
    }

    static BufferedReader in;
    static PrintWriter out;
    static StringTokenizer tok;

    public static void main(String[] args) throws IOException {
        in = new BufferedReader(new InputStreamReader(System.in));
        out = new PrintWriter(System.out);
        tok = new StringTokenizer("");
        Main main = new Main();
        main.solve();
        out.close();
    }
}