import java.util.Arrays;
import java.util.Scanner;

class Main {
    static Scanner in = new Scanner(System.in);

    public static void main(String[] args) {
        int N = in.nextInt(), M = in.nextInt(), K = in.nextInt();
        int[] a = new int[M + 1], b = new int[M + 1], c = new int[M + 1];
        for (int i = 1; i < M + 1; i++) {
            a[i] = in.nextInt();
            b[i] = in.nextInt();
            c[i] = in.nextInt();
        }
        int[] d = new int[K + 1];
        for(int i = 1; i < K + 1; i++){
            d[i] = in.nextInt();
        }
        boolean[][] n = new boolean[K + 1][N + 1];
        Arrays.fill(n[0], true);
        for(int i = 1; i < K + 1; i++){
            Arrays.fill(n[i], false);
        }
        
        for(int x = 1; x < K + 1; x++){
            for(int y = 1; y < N + 1; y++){
                for(int z = 1; z < M + 1; z++){
                    if(n[x - 1][y]){
                        if(a[z] == y && c[z] == d[x]){
                            n[x][b[z]] = true;
                        }
                        if(b[z] == y && c[z] == d[x]){
                            n[x][a[z]] = true;
                        }
                    }
                }
            }
        }
        int sum = 0;
        for(int i = 1; i < N + 1; i++){
            if(n[K][i]){
                sum++;
            }
        }
        System.out.println(sum);
        boolean t = true;
        for(int i = 1; i < N + 1; i++){
            if(t && n[K][i]){
                System.out.print(i);
                t = false;
            }else if(n[K][i]){
                System.out.print(" " + i);
            }
        }
        System.out.println();
    }
}