using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Yukicoder
{
    class Program
    {
        private class Edge
        {
            private readonly int _from;
            private readonly int _to;

            public Edge(int from, int to)
            {
                _from = @from;
                _to = to;
            }

            public int From
            {
                get { return _from; }
            }

            public int To
            {
                get { return _to; }
            }
        }

        static void Main(string[] args)
        {
            var line = Console.ReadLine().Split(' ').Select(long.Parse).ToArray();
            var n = line[0];
            var m = line[1];
            var k = line[2];

            Dictionary<long, List<Edge>> map = new Dictionary<long, List<Edge>>();
            for (int i = 0; i < m; i++)
            {
                var edge = Console.ReadLine().Split(' ').Select(long.Parse).ToArray();
                if (!map.ContainsKey(edge[2]))
                {
                    map.Add(edge[2], new List<Edge>());                    
                }
                map[edge[2]].Add(new Edge((int)edge[0], (int)edge[1]));
            }
            var history = Console.ReadLine().Split(' ').Select(long.Parse).ToArray();
            var list = new List<Dictionary<int, List<int>>>();
            for (int i = 0; i < history.Length; i++)
            {
                var cost = history[i];
                var candidates = new Dictionary<int, List<int>>();
                for (int j = 0; j < map[cost].Count; j++)
                {
                    if (!candidates.ContainsKey(map[cost][j].From))
                    {
                        candidates.Add(map[cost][j].From, new List<int>());
                    }
                    candidates[map[cost][j].From].Add(map[cost][j].To);
                    if (!candidates.ContainsKey(map[cost][j].To))
                    {
                        candidates.Add(map[cost][j].To, new List<int>());
                    }
                    candidates[map[cost][j].To].Add(map[cost][j].From);
                }
                list.Add(candidates);
            }
            int[] previous = list[0].SelectMany(element=>element.Value).Distinct().ToArray();
            for (int i = 1; i < list.Count; i++)
            {
                List<int> nexts = new List<int>();
                for (int j = 0; j < previous.Length; j++)
                {
                    if (list[i].ContainsKey(previous[j]))
                    {
                        nexts.AddRange(list[i][previous[j]]);                        
                    }
                }
                previous = nexts.Distinct().ToArray();
            }
            Array.Sort(previous);
            Console.WriteLine(previous.Length);
            Console.WriteLine(string.Join(" ",previous));
        }
    }
}