package yukicoder;

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

public class P92 {

	public static void main(String[] args) throws IOException {
		MyScanner sc = new MyScanner(System.in);
		PrintWriter pw=new PrintWriter(System.out);
		final int n = sc.nextInt(); final int m = sc.nextInt(); final int k = sc.nextInt();
		HashMap<Integer, ArrayList<Edge>> adj = new HashMap<>(n+1);
		for(int i=1; i<=n; i++) {
			adj.put(i, new ArrayList<Edge>());
		}
		for(int i=0; i<m; i++) {
			int a = sc.nextInt(); int b = sc.nextInt(); int c = sc.nextInt();
			adj.get(a).add(new Edge(b, c));
			adj.get(b).add(new Edge(a, c));
		}
		int[] ds = new int[k+1];
		for(int i=1; i<=k; i++) {
			ds[i] = sc.nextInt();
		}
		boolean[][] exists = new boolean[k+1][n+1];
		Arrays.fill(exists[0], true);
		for(int t=1; t<=k; t++) {
			for(int i=1; i<=n; i++) {
				if(exists[t-1][i]) {
					for(Edge e : adj.get(i)) {
						if(ds[t] == e.w) {
							exists[t][e.to] = true;
						}
					}
				}
			}
		}
		int cnt = 0;
		ArrayList<Integer> ans = new ArrayList<>();
		for(int i=1; i<=n; i++) {
			if(exists[k][i]) {
				cnt++;
				ans.add(i);
			}
		}
		pw.println(cnt);
		for(int i=0; i<cnt; i++) {
			if(i==0) {
				pw.print(ans.get(i));
			} else {
				pw.print(" " + ans.get(i));
			}
		}
		pw.println();
		pw.close();
	}
	
	static class Edge {
		int to;
		int w;
		Edge(int _to, int _w) {
			to = _to; w = _w;
		}
	}

	static class MyScanner
	{
		BufferedReader br;
		StringTokenizer st;
		public MyScanner(InputStream s)
		{
			br=new BufferedReader(new InputStreamReader(s));
		}
		public String nextLine() throws IOException
		{
			return br.readLine();
		}
		public String next() throws IOException
		{
			while(st==null || !st.hasMoreTokens())
				st=new StringTokenizer(br.readLine());
			return st.nextToken();
		}
		public int nextInt() throws IOException
		{
			return Integer.parseInt(next());
			
		}
		public double nextDouble() throws IOException
		{
			return Double.parseDouble(next());
		}
		public boolean ready() throws IOException
		{
			return br.ready();
		}
		public long nextLong() throws IOException
		{
			return Long.parseLong(next());
		}
	}
}