#include <bits/stdc++.h>
using namespace std;
int main(){
  int N, M, K;
  cin >> N >> M >> K;
  vector<vector<pair<int, int>>> E(N);
  for (int i = 0; i < M; i++){
    int a, b, c;
    cin >> a >> b >> c;
    a--;
    b--;
    E[a].push_back(make_pair(c, b));
    E[b].push_back(make_pair(c, a));
  }
  vector<int> d(K);
  for (int i = 0; i < K; i++){
    cin >> d[i];
  }
  vector<vector<bool>> dp(K + 1, vector<bool>(N, false));
  for (int i = 0; i < N; i++){
    dp[0][i] = true;
  }
  for (int i = 0; i < K; i++){
    for (int j = 0; j < N; j++){
      if (dp[i][j]){
        for (auto P : E[j]){
          if (P.first == d[i]){
            dp[i + 1][P.second] = true;
          }
        }
      }
    }
  }
  vector<int> ans;
  for (int i = 0; i < N; i++){
    if (dp[K][i]){
      ans.push_back(i);
    }
  }
  int cnt = ans.size();
  cout << cnt << endl;
  for (int i = 0; i < cnt; i++){
    cout << ans[i] + 1;
    if (i < cnt - 1){
      cout << ' ';
    }
  }
  cout << endl;
}