#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<ll> VL;
typedef vector<VL> VVL;
typedef pair<int, int> PII;

#define FOR(i, a, n) for (int i = (int)a; i < (int)n; ++i)
#define REP(i, n) FOR(i, 0, n)
#define ALL(x) x.begin(), x.end()
#define MOD 1000000007
#define INF 1000000000
#define PI 3.14159265359
#define EPS 1e-12

int main(void)
{
  int n, m, k, d[1005];
  vector<PII> g[105];
  cin >> n >> m >> k;
  REP(i, m) {
    int a, b, c;
    cin >> a >> b >> c;
    a--; b--;
    g[a].push_back(make_pair(c, b));
    g[b].push_back(make_pair(c, a));
  }
  REP(i, k) cin >> d[i];

  int vis[2][101];
  REP(i, n) vis[0][i] = 1;

  REP(i, k) {
    int cur=i%2, tar=cur^1;
    REP(j, n) vis[tar][j] = 0;
    /*REP(i, n) cout << vis[0][i] << " "; cout << endl;
    REP(i, n) cout << vis[1][i] << " "; cout << endl;*/
    REP(j, n) if(vis[cur][j]) {
      for(PII l: g[j]) {
        //cout << d[i] << " " << l.first << " " << l.second << endl;
        if(d[i] == l.first) vis[tar][l.second] = 1;
      }
    }
    /*REP(i, n) cout << vis[0][i] << " "; cout << endl;
    REP(i, n) cout << vis[1][i] << " "; cout << endl;*/
  }

  int num = 0;
  REP(i, n) if(vis[k%2][i]) num++;
  cout << num << endl;
  REP(i, n) if(vis[k%2][i]) {
    cout << i+1 << " ";
  }
  cout << endl;

  return 0;
}