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

#ifdef LOCAL
    #define eprintf(...) fprintf(stderr, __VA_ARGS__)
#else
        #define eprintf(...) 42
#endif

#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define repi(i,a,b) for(int i=(int)(a);i<(int)(b);i++)
#define all(x) (x).begin(),(x).end()
#define foreach(u,v) for(auto (u) : (v))
#define pb push_back
#define mp make_pair
#define mt make_tuple

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef pair<ll, ll> pll;
typedef vector<ll> vl;

const int inf = 1e9;
const ll linf = 1LL<<60;
const ll mod = 1e9 + 7;
const double eps = 1e-9;

/*
*/

int main()
{
  int n, m, k;
  cin >> n >> m >> k;

  vector<pii> g[n];
  rep(i, m){
    int a, b, c;
    cin >> a >> b >> c;
    a--; b--;
    g[a].pb({b, c});
    g[b].pb({a, c});
  }

  vi d(k);
  rep(i, k) cin >> d[i];

  set<int> from, to;
  rep(i, n) from.insert(i);

  rep(i, k){
    for(auto f : from){
      for(auto e : g[f]){
        if(e.second == d[i]){
          to.insert(e.first);
        }
      }
    }
    from.swap(to);
    to.clear();
  }

  cout << from.size() << endl;
  bool flag = false;
  for(auto i : from){
    if(flag) cout << " ";
    cout << i+1;
    flag = true;
  }
  cout << endl;

  return 0;
}