using System;
using System.Collections;
using System.Collections.Generic;
 
class TEST{
	static void Main(){
		Sol mySol =new Sol();
		mySol.Solve();
	}
}

class Sol{
	public void Solve(){
		
		Dictionary<int,List<Pair>> D=new Dictionary<int,List<Pair>>();
		for(int i=0;i<M;i++){
			if(!D.ContainsKey(info[i][2]))D.Add(info[i][2],new List<Pair>());
			D[info[i][2]].Add(new Pair(info[i][0],info[i][1]));
		}
		
		HashSet<int>[] H=new HashSet<int>[2];
		H[0]=new HashSet<int>();
		foreach(Pair p in D[route[0]]){
			H[0].Add(p.to);
		}
		
		int now=0;
		int next=0;
		for(int i=0;i<M;i++){
			now=i%2;
			next=1-now;
			H[next]=new HashSet<int>();
			if(i==0){
				foreach(Pair p in D[route[i]]){
					H[next].Add(p.to);
					H[next].Add(p.from);
				}
				continue;
			}
			foreach(Pair p in D[route[i]]){
				if(H[now].Contains(p.from))H[next].Add(p.to);
				if(H[now].Contains(p.to))H[next].Add(p.from);
			}
		}
		
		
		List<int> L=new List<int>(H[next]);
		L.Sort();
		
		Console.WriteLine(L.Count);
		for(int i=0;i<L.Count;i++){
			Console.Write(i==0?"{0}":" {0}",L[i]);
		}
		Console.WriteLine();
		
		
		
		
		
		
		
	}
	int N,M,K;
	int[][] info;
	int[] route;
	public Sol(){
		var d=ria();
		N=d[0];M=d[1];K=d[2];
		info=new int[M][];
		for(int i=0;i<M;i++)info[i]=ria();
		route=ria();
		
	}
	class Pair{
		public int from;
		public int to;
		public Pair(int f,int t){
			from=f;
			to=t;
		}
	}




	static String rs(){return Console.ReadLine();}
	static int ri(){return int.Parse(Console.ReadLine());}
	static long rl(){return long.Parse(Console.ReadLine());}
	static double rd(){return double.Parse(Console.ReadLine());}
	static String[] rsa(){return Console.ReadLine().Split(' ');}
	static int[] ria(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>int.Parse(e));}
	static long[] rla(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>long.Parse(e));}
	static double[] rda(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>double.Parse(e));}
}