#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];
bool visit[2][110];
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) visit[0][i]=true;
	REP(k,0,K){
		int now=k%2;
		REP(i,0,N) visit[1-now][i]=false;
		REP(i,0,N){
			if(visit[now][i]){
				REP(j,0,edge[i].size()){
					if(edge[i][j].S==d[k]) {
						visit[1-now][edge[i][j].F]=true;
					}
				}
			}
		}
	}
	cout<<count(visit[K%2],visit[K%2]+N,true)<<endl;

	bool flag=false;
	REP(i,0,N){
		if(!visit[K%2][i]) continue;
		if(!flag) {
			cout<<i+1;
			flag=true;
		}
		else cout<<" "<<i+1;
	}
	cout<<endl;
	return 0;
}