import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.List;
import java.util.Queue;
import java.util.Scanner;
import java.util.Set;
import java.util.TreeSet;


public class Main_yukicoder92 {

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);

        int n = sc.nextInt();
        int m = sc.nextInt();
        int k = sc.nextInt();
        List<Queue<Edge>> edges = new ArrayList<Queue<Edge>>();
        for (int i = 0; i < n; i++) {
        	edges.add(new ArrayDeque<Edge>());
        }
        for (int i = 0; i < m; i++) {
        	int a = sc.nextInt() - 1;
        	int b = sc.nextInt() - 1;
        	int c = sc.nextInt();

        	edges.get(a).add(new Edge(a, b, c));
        	edges.get(b).add(new Edge(b, a, c));
        }

        int[] d = new int[k];
        for (int i = 0; i < k; i++) {
        	d[i] = sc.nextInt();
        }

    	Set<Integer> ret = new TreeSet<Integer>();
    	for (int i = 0; i < n; i++) {
    		ret.add(i);
    	}

    	for (int i = 0; i < k; i++) {
    		Set<Integer> tmp = new TreeSet<Integer>();
    		for (int v : ret) {
        		for (Edge e : edges.get(v)) {
        			if (e.w == d[i]) {
        				tmp.add(e.v);
        			}
        		}

    		}
    		ret = tmp;
    	}

        System.out.println(ret.size());
        boolean flag = false;
        for (int e : ret) {
        	if (!flag) {
        		System.out.printf("%d", e + 1);
        		flag = true;
        	} else {
        		System.out.printf(" %d", e + 1);
        	}
        }
        System.out.println("");

        sc.close();
    }

	private static class Edge {
//		int u; // from
		int v; // to
		int w; // cost

		Edge(int u, int v, int w) {
//			this.u = u;
			this.v = v;
			this.w = w;
		}
	}
}