using System;
using System.IO;
using System.Text;
using System.Linq;
using System.Diagnostics;
using System.Collections.Generic;
using Enu = System.Linq.Enumerable;

class Program
{
    void Solve()
    {
        int N = reader.Int(), M = reader.Int(), K = reader.Int();
        var dic = Enu.Range(0, N).Select(a => new Dictionary<int, HashSet<int>>()).ToArray();

        for (int i = 0; i < M; i++)
        {
            int a = reader.Int() - 1, b = reader.Int() - 1, c = reader.Int();
            Add(a, b, c, dic);
            Add(b, a, c, dic);
        }
        bool[] can = Enu.Repeat(true, N).ToArray();
        foreach (var c in reader.IntArray(K))
        {
            bool[] next = new bool[N];
            for (int a = 0; a < N; a++)
                if (can[a] && dic[a].ContainsKey(c))
                    foreach (var b in dic[a][c])
                        next[b] = true;
            can = next;
        }

        var ans = Enu.Range(0, N).Where(a => can[a]).Select(a => a + 1);
        Console.WriteLine(ans.Count() + "\n" + string.Join(" ", ans));
        Console.ReadLine();
    }

    void Add(int a, int b, int c, Dictionary<int, HashSet<int>>[] dic)
    {
        if (!dic[a].ContainsKey(c)) dic[a][c] = new HashSet<int>();
        dic[a][c].Add(b);
    }


    static void Main() { new Program().Solve(); }
    Reader reader = new Reader(Console.In);
    class Reader
    {
        private readonly TextReader reader;
        private readonly char[] separator = { ' ' };
        private readonly StringSplitOptions removeOp = StringSplitOptions.RemoveEmptyEntries;
        private string[] A = new string[0];
        private int i;

        public Reader(TextReader r) { reader = r; }
        public bool HasNext() { return Enqueue(); }
        public string String() { return Dequeue(); }
        public int Int() { return int.Parse(Dequeue()); }
        public long Long() { return long.Parse(Dequeue()); }
        public double Double() { return double.Parse(Dequeue()); }
        public int[] IntLine() { var s = Line(); return s == "" ? new int[0] : Array.ConvertAll(Split(s), int.Parse); }
        public int[] IntArray(int N) { return Enu.Range(0, N).Select(i => Int()).ToArray(); }
        public int[][] IntGrid(int H) { return Enu.Range(0, H).Select(i => IntLine()).ToArray(); }
        public string[] StringArray(int N) { return Enu.Range(0, N).Select(i => Line()).ToArray(); }
        public string Line() { return reader.ReadLine().Trim(); }
        private string[] Split(string s) { return s.Split(separator, removeOp); }
        private bool Enqueue()
        {
            if (i < A.Length) return true;
            string line = reader.ReadLine();
            if (line == null) return false;
            if (line == "") return Enqueue();
            A = Split(line);
            i = 0;
            return true;
        }
        private string Dequeue() { Enqueue(); return A[i++]; }
    }
}