#include<iostream>
#include<vector>
#include<string>
#include<algorithm>	
#include<map>
#include<set>
#include<utility>
#include<cmath>
#include<cstring>
#include<queue>
#include<stack>
#include<cstdio>
#include<sstream>
#include<iomanip>
#include<assert.h>
#define loop(i,a,b) for(int i=a;i<b;i++) 
#define rep(i,a) loop(i,0,a)
#define pb push_back
#define mt make_tuple
#define all(in) in.begin(),in.end()
#define shosu(x) fixed<<setprecision(x)
using namespace std;
//kaewasuretyuui
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vp;
typedef vector<vp> vvp;
typedef vector<string> vs;
typedef vector<double> vd;
typedef tuple<int,int,int> tp;
typedef vector<tp> vt;
typedef vector<vd> vvd;
typedef pair<int,pii> pip;
typedef vector<pip>vip;
const double PI=acos(-1);
const double EPS=1e-7;
const int inf=1e8;
const ll INF=1e16;
int dx[]={0,1,0,-1};
int dy[]={1,0,-1,0};
int main(){
	int n,m,k;
	cin>>n>>m>>k;
	vvp G(n);
	rep(i,m){
		int a,b,c;
		cin>>a>>b>>c;
		a--;b--;
		G[a].pb(pii(b,c));
		G[b].pb(pii(a,c));
	}
	vi dp(n,1);
	rep(i,k){
		int a;cin>>a;
		vi ndp(n);
		rep(j,n)if(dp[j]){
			rep(k,G[j].size())if(G[j][k].second==a){
				ndp[G[j][k].first]=true;
			}
		}
		dp=ndp;
	}
	vi out;
	rep(i,n)if(dp[i])out.pb(i+1);
	cout<<out.size()<<endl;
	rep(i,out.size())cout<<out[i]<<" ";
	cout<<endl;
}