#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <complex>
#include <queue>
#include <set>
#include <map>
#include <unordered_map>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

typedef long long ll;

int main() {

  int N, M, K; cin >> N >> M >> K;
  unordered_map<int, unordered_map<int, vector<int>>> cab;
  rep(i, M) {
    int a, b, c; cin >> a >> b >> c;
    cab[c][a].push_back(b);
    cab[c][b].push_back(a);
  }
  vector<int> d(K);
  rep(i, K) {
    cin >> d[i];
  }

  vector<int> now[1001];
  rep(i, N) now[0].push_back(i+1);
  rep(i, K) {
    auto& ab = cab[d[i]];
    rep(pre, N) {
      vector<int> next;
      rep(k, now[pre].size()) {
        auto& tar = ab[now[pre][k]];
        std::copy(tar.begin(), tar.end(), back_inserter(next));
      }
      std::sort(next.begin(), next.end());
      next.erase(std::unique(next.begin(), next.end()), next.end());
      now[pre] = next;
    }
  }

  vector<int> ans;  
  rep(i, N) {
    rep(j, now[i].size()) {
      ans.push_back(now[i][j]);
    }
  }

  std::sort(ans.begin(), ans.end());

  cout << ans.size() << endl;
  rep(i, ans.size()) {
    if(i) cout << " ";
    cout << ans[i];
  }
  cout << endl;

  return 0;
}