#include <bits/stdc++.h>
#define REP(a,b,c) for(int a=b; a<(int)c; a++)
#define rep(a,b) REP(a,0,b)
typedef long long int llint;
using namespace std;

int main(){
  int N, M, K;
  cin >> N >> M >> K;
  vector < pair<int,int> > dp[N+1];
  rep(i,M){
	int a,b,c;
	cin >> a >> b >> c;
	dp[a].push_back(pair<int, int>(b,c));
	dp[b].push_back(pair<int, int>(a,c));
  }
  vector <int> d;
  rep(i,K){
	int tmp;
	cin >> tmp;
	d.push_back(tmp);
  }
  vector <bool> tmp1(N+1,true);
  rep(i,d.size()){//nedan
	//	rep(j,tmp1.size())if(tmp1[j]) cout << j << ", ";
	//	cout << endl;
	vector <bool> tmp2(N+1, false);
	rep(l, N+1){//pos
	  if(!tmp1[l]) continue;
	  rep(j, dp[l].size()){
		if(dp[l][j].second == d[i]){
		  // cout << l << ", " << dp[l][j].first << endl;
		  tmp2[dp[l][j].first] = true;
		}
	  }
	}
	rep(j,tmp1.size())tmp1[j] = tmp2[j];
  }
  
  int cnt = 0;
  rep(i,N+1) if(tmp1[i]) cnt++;
  cout << cnt << endl;
  rep(i,N+1)if(tmp1[i]) cout << i << " ";
  cout << endl;

  return 0;
}