// Enjoy your stay.

#include <bits/stdc++.h>

#define EPS 1e-9
#define INF 1070000000LL
#define MOD 1000000007LL
#define fir first
#define foreach(it,X) for(auto it=(X).begin();it!=(X).end();it++)
#define ite iterator
#define mp make_pair
#define mt make_tuple
#define rep(i,n) rep2(i,0,n)
#define rep2(i,m,n) for(int i=m;i<(n);i++)
#define pb push_back
#define sec second
#define sz(x) ((int)(x).size())

using namespace std;

typedef istringstream iss;
typedef long long ll;
typedef pair<ll,ll> pi;
typedef stringstream sst;
typedef vector<ll> vi;

int dp[1111][111];
vector<pi> g[111];

int main(){
	cin.tie(0);
	ios_base::sync_with_stdio(0);
	
	int N,M,K;
	cin>>N>>M>>K;
	rep(i,M){
		int a,b,c;
		cin>>a>>b>>c;a--;b--;
		g[a].pb(mp(b,c));
		g[b].pb(mp(a,c));
	}
	rep(i,N)dp[0][i] = 1;
	rep(i,K){
		int d;
		cin>>d;
		rep(j,N)if(dp[i][j]){
			rep(k,sz(g[j]))if(g[j][k].sec == d){
				dp[i+1][g[j][k].fir] = 1;
			}
		}
	}
	vi ans;
	rep(i,N)if(dp[K][i])ans.pb(i+1);
	cout<<sz(ans)<<endl;
	rep(i,sz(ans))cout<<ans[i]<<(i==sz(ans)-1?"\n":" ");
}