import java.util.*;

public class Main {
  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[] a = new int[M];
    int[] b = new int[M];
    int[] c = new int[M];
    int[] d = new int[K];
    for(int i = 0; i < M; i++) {
      a[i] = sc.nextInt() - 1;
      b[i] = sc.nextInt() - 1;
      c[i] = sc.nextInt();
    }
    for(int i = 0; i < K; i++) {
      d[i] = sc.nextInt();
    }
    // dp[i][j]はd1～di(i個)までから町jが可能性があるかどうかを表す
    int[][] dp = new int[K + 1][N];
    for(int j = 0; j < N; j++) {
      dp[0][j] = 1;
    }
    for(int i = 1; i < K + 1; i++) {
      for(int k = 0; k < M; k++) {
        if(c[k] == d[i - 1]) {
          int towna = a[k];
          int townb = b[k];
          if(dp[i][towna] == 0) {
            dp[i][towna] = dp[i - 1][townb];
          }
          if(dp[i][townb] == 0) {
            dp[i][townb] = dp[i - 1][towna];
          }
        }
      }
    }
    int ans = 0;
    for(int j = 0; j < N; j++) {
      ans += dp[K][j];
    }
    System.out.println(ans);
    ArrayList<Integer> town = new ArrayList<Integer>();
    for(int j = 0; j < N; j++) {
      if(dp[K][j] == 1) town.add(j + 1);
    }
    for(int j = 0; j < town.size(); j++) {
      System.out.print(town.get(j));
      if(j < town.size() - 1) {
        System.out.print(" ");
      } else {
        System.out.println();
      }
    }
  }
}