package yukicoder244;
import java.util.Scanner;
import java.util.TreeSet;
public class Main {
	public static void main(String[] args){
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();//the number of the cities
		int m=sc.nextInt();//the number of the roads
		int k=sc.nextInt();//
		int[] a=new int[m];
		int[] b=new int[m];
		int[] c=new int[m];
		
		for(int i=0;i<m;i++){
			a[i]=sc.nextInt();//city number
			b[i]=sc.nextInt();//city number
			c[i]=sc.nextInt();//toll
		}
		int[] d=new int[k+1];
		for(int i=1;i<k+1;i++){
			d[i]=sc.nextInt();//record
		}
		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 i=2;i<=k;i++){
			for(int j=0;j<m;j++){
				if(c[j]==d[i]){
					if(dp[i-1][a[j]]==1)dp[i][b[j]]=1;
					if(dp[i-1][b[j]]==1)dp[i][a[j]]=1;
				}
			}
		}
		TreeSet<Integer> ret=new TreeSet<Integer>();
		for(int i=1;i<=n;i++){
			if(dp[k][i]==1)ret.add(i);
		}
		System.out.println(ret.size());
		int count=0;
		for(Integer r:ret){
			count++;
			System.out.print(r);
			if(count!=ret.size())System.out.print(" ");
		}
		System.out.println();
		sc.close();
	}
}