#include <bits/stdc++.h>
using namespace std;

#define rep(i,j,n) for(int i=j;i<n;++i)
#define all(i) i.begin(),i.end()
#define rall(i) i.rbegin(), i.rend()
#define INF 1e9
#define LINF 1e18
const int mod = 1e9 + 7;

typedef long long i64;
typedef pair<int, int> pi;

template <class T> using vt = vector<T>;
template <class T> using vvt = vector<vector<T>>;

i64 gcd(i64 n, i64 m) {return (m == 0? n : gcd(m, n % m));}
i64 lcd(i64 n, i64 m) {return (n / gcd(n, m) * m);}
int dx[] = {1, 0, -1, 0};
int dy[] = {0, 1, 0, -1};

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

  int n, m, k;
  cin >> n >> m >> k;
  vt<pair<pi, int>> edge(m);
  rep(i, 0, m) {
    int a, b, c;
    cin >> a >> b >> c;
    edge.push_back({{a, b}, c});
  }
  vt<int> d(k);
  rep(i, 0, k) cin >> d[i];

  vvt<bool> dp(k + 1, vt<bool>(n + 1, false));
  rep(i, 1, n + 1) dp[0][i] = true;
  rep(i, 0, k) {
    for(auto &it : edge) {
      if(dp[i][it.first.first] && d[i] == it.second) dp[i + 1][it.first.second] = true;
      if(dp[i][it.first.second] && d[i] == it.second) dp[i + 1][it.first.first] = true;
    }
  }

  vt<int> ans;
  rep(i, 1, n + 1) {
    if(dp[k][i]) ans.push_back(i);
  }
  cout << ans.size() << endl;
  rep(i, 0, ans.size()) cout << ans[i] << " \n"[i == ans.size() - 1];
}