#include <bits/stdc++.h>

using namespace std;

#define REP(i,n) for(int i=0; i<(int)(n); i++)
#define FOR(i,b,e) for (int i=(int)(b); i<(int)(e); i++)
#define ALL(x) (x).begin(), (x).end()

const double PI = acos(-1);

int n, m, k;
vector<pair<int, int> > edges[100];
bool dp[1001][100];

int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);

  cin >> n >> m >> k;
  REP (i, m) {
    int a, b, c;
    cin >> a >> b >> c;
    --a, --b;
    edges[a].emplace_back(b, c);
    edges[b].emplace_back(a, c);
  }

  vector<int> d(k);
  REP (i, k) cin >> d[i];
  
  REP (i, n) dp[0][i] = true;
  REP (i, k) REP (j, n) {
    if (!dp[i][j]) continue;
    for (auto &pr: edges[j]) {
      if (pr.second == d[i]) {
        dp[i+1][pr.first] = true;
      }
    }
  }
  vector<int> ret;
  REP (i, n) if (dp[k][i]) ret.push_back(i+1);

  cout << ret.size() << endl;
  for (int x: ret)
    cout << x << " ";
  cout << endl;
  
  return 0;
}