import java.io.*;
import java.util.*;

public class Main {
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        int m = sc.nextInt();
        int k = sc.nextInt();
        TreeSet<Integer> current = new TreeSet<>();
        ArrayList<ArrayList<Path>> graph = new ArrayList<>();
        for (int i = 0; i < n; i++) {
            current.add(i);
            graph.add(new ArrayList<>());
        }
        for (int i = 0; i < m; i++) {
            int a = sc.nextInt() - 1;
            int b = sc.nextInt() - 1;
            int c = sc.nextInt();
            graph.get(a).add(new Path(b, c));
            graph.get(b).add(new Path(a, c));
        }
        while (k-- > 0) {
            int x = sc.nextInt();
            TreeSet<Integer> next = new TreeSet();
            for (int y : current) {
                for (Path z : graph.get(y)) {
                    if (z.value == x) {
                        next.add(z.idx);
                    }
                }
            }
            current = next;
        }
        StringBuilder sb = new StringBuilder();
        sb.append(current.size()).append("\n");
        boolean isFirst = true;
        for (int x : current) {
            if (!isFirst) {
                sb.append(" ");
            }
            isFirst = false;
            sb.append(x + 1);
        }
        System.out.println(sb);
    }
    
    static class Path {
        int idx;
        int value;
        
        public Path(int idx, int value) {
            this.idx = idx;
            this.value = value;
        }
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}