import java.util.ArrayList;
import java.util.HashSet;
import java.util.Scanner;
import java.util.TreeSet;

public class Main {
	static int N, M, K;
	static int[] A, B, C;
	static int[] D;
	
	public static int solve(){
		int[][] dp = new int[K+1][N+1];
		for (int i = 0; i < K+1; i++) {
			for (int j = 0; j < N+1; j++) {
				dp[i][j] = 0;
			}
		}
		
		for (int i = 0; i < M; i++) {
			if(C[i] == D[1]) dp[1][A[i]] = dp[1][B[i]] = 1;
		}
		
		for (int k = 2; k <= K; k++) {
			for (int i = 0; i < M; i++) {
				if(C[i] == D[k])
				{
					if(dp[k-1][A[i]] == 1) dp[k][B[i]] = 1;
					if(dp[k-1][B[i]] == 1) dp[k][A[i]] = 1;
				}
			}
		}
		
		TreeSet<Integer> ret = new TreeSet<Integer>();
		for (int i = 1; i <= N; i++) {
			if(dp[K][i] == 1) ret.add(new Integer(i));
		}
		
		System.out.println(ret.size());
		
		int count = 0;
		for (Integer i : ret) {
			System.out.print(i);
			count++;
			if(count != ret.size()) System.out.print(" ");
		}
		
		System.out.print("\n");
		
		return 0;
	}
	
	public static void main(String[] args){
		Scanner S = new Scanner(System.in);
		
		N = S.nextInt();
		M = S.nextInt();
		K = S.nextInt();
		
		A = new int[M];
		B = new int[M];
		C = new int[M];
		for (int i = 0; i < M; i++) {
			A[i] = S.nextInt();
			B[i] = S.nextInt();
			C[i] = S.nextInt();
		}
		
		D = new int[K+1];
		for (int i = 1; i < K+1; i++) {
			D[i] = S.nextInt();
		}
		
		solve();
	}
}