#include <bits/stdc++.h>
#define REP(i,n,N) for(int i=(n);i<(int) N;i++)
#define F first
#define S second
using namespace std;

vector<pair<int,int>> edge[110];
vector<int> ok;
int d[1010];
int main() {
	int N,M,K;
	cin>>N>>M>>K;
	REP(i,0,M){
		int a,b,c;
		cin>>a>>b>>c;
		a--;b--;
		edge[a].push_back({b,c});
		edge[b].push_back({a,c});
	}
	REP(i,0,K) cin>>d[i];
	REP(i,0,N) ok.push_back(i);
	REP(k,0,K){
		vector<int> tmp;
		for(auto next:ok){
			REP(j,0,edge[next].size()){
				if(edge[next][j].S==d[k]) tmp.push_back(edge[next][j].F);
			}
		}
		tmp.erase(unique(tmp.begin(),tmp.end()),tmp.end());
		ok=tmp;
	}
	cout<<ok.size()<<endl;
	sort(ok.begin(),ok.end());
	bool flag=false;
	for(auto v:ok)	{
		if(!flag) {
			cout<<v+1;
			flag=true;
		}
		else cout<<" "<<v+1;
	}
	cout<<"";
	return 0;
}