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

class Program
{
    public void Proc()
    {
        Reader.IsDebug = false;
        int[] inpt = Reader.GetInt();

        int matiCount = inpt[0];

        int roadCount = inpt[1];

        int queryCount = inpt[2];

        List<Road> roadList = new List<Road>();

        for (int i = 0; i < roadCount; i++)
        {
            inpt = Reader.GetInt();
            Road rd = new Road(inpt[0], inpt[1], inpt[2]);
            roadList.Add(rd);
        }

        int[] history = Reader.GetInt();

        List<int> target = new List<int>();

        roadList.FindAll((a) =>
        {
            return (a.Cost == history[0]);
        }).ForEach((a) =>
        {
            if (!target.Contains(a.Mati1))
            {
                target.Add(a.Mati1);
            }
            if (!target.Contains(a.Mati2))
            {
                target.Add(a.Mati2);
            }
        });

        for (int i = 1; i < history.Length; i++)
        {
            List<int> nextTarget = new List<int>(); ;
            target.ForEach((a) => {
                roadList.FindAll((b) =>
                {
                    return (b.Mati1 == a || b.Mati2 == a) && b.Cost == history[i];
                }).ForEach((c) => {
                    if (c.Mati1 != a && (!nextTarget.Contains(c.Mati1)))
                    {
                        nextTarget.Add(c.Mati1);
                    } else if(c.Mati2 != a && (!nextTarget.Contains(c.Mati2))) {
                        nextTarget.Add(c.Mati2);
                    }
                });
            });
            target = nextTarget;
            if (nextTarget.Count == 0)
            {
                break;
            }
        }
        target.Sort();
        Console.WriteLine(target.Count);
        Console.WriteLine(string.Join<int>(" ", target)); 
    
    }

    public class Road
    {
        public int Mati1;
        public int Mati2;
        public int Cost;

        public Road(int m1, int m2, int c)
        {
            this.Mati1 = m1;
            this.Mati2 = m2;
            this.Cost = c;
        }
    }


    public class Reader
    {
        public static bool IsDebug = true;
        private static String PlainInput = @"

3 2 2
1 2 10
1 2 20
10 20





 
";
        private static System.IO.StringReader Sr = null;
        public static string ReadLine()
        {
            if (IsDebug)
            {
                if (Sr == null)
                {
                    Sr = new System.IO.StringReader(PlainInput.Trim());
                }
                return Sr.ReadLine();
            }
            else
            {
                return Console.ReadLine();
            }
        }
        public static int[] GetInt(char delimiter = ' ', bool trim = false)
        {
            string inptStr = ReadLine();
            if (trim)
            {
                inptStr = inptStr.Trim();
            }
            string[] inpt = inptStr.Split(delimiter);
            int[] ret = new int[inpt.Length];
            for (int i = 0; i < inpt.Length; i++)
            {
                ret[i] = int.Parse(inpt[i]);
            }
            return ret;
        }
    }
    static void Main()
    {
        Program prg = new Program();
        prg.Proc();
    }
}