import java.util.*;

public class Exercise134{
  public static void main (String[] args){

    Scanner sc = new Scanner(System.in);

    int n = sc.nextInt();
    int m = sc.nextInt();
    int k = sc.nextInt();
    int[][] r = new int[m][3];
    for(int i = 0; i < m; i++){
      r[i][0] = sc.nextInt();
      r[i][1] = sc.nextInt();
      r[i][2] = sc.nextInt();
    }
    int[] p = new int[k];
    for(int i = 0; i < k; i++){
      p[i] = sc.nextInt();
    }
    boolean[][] dp = new boolean[2][n + 1];
    for(int i = 0; i < m; i++){
      if(r[i][2] == p[0]){
        dp[0][r[i][0]] = true;
        dp[0][r[i][1]] = true;
      }
    }
    for(int i = 1; i < k; i++){
      Arrays.fill(dp[i % 2], false);
      for(int j = 0; j < m; j++){
        if(r[j][2] == p[i]){
          if(dp[(i - 1) % 2][r[j][0]]){
            dp[i % 2][r[j][1]] = true;
          }
          if(dp[(i - 1) % 2][r[j][1]]){
            dp[i % 2][r[j][0]] = true;
          }
        }
      }
    }
    int count = 0;
    String s = "";
    for(int i = 1; i < n + 1; i++){
      if(dp[(k - 1) % 2][i]){
        count++;
        s += i + " ";
      }
    }
    System.out.println(count);
    System.out.println(s);
  }
}