#include <ctime>
#include <iostream>// io
#include <iomanip>
#include <fstream>
#include <sstream>
#include <vector>// container
#include <map>
#include <set>
#include <queue>
#include <bitset>
#include <stack>
#include <algorithm>// other
#include <utility>
#include <complex>
#include <numeric>
#include <functional>
#include <random>
#include <regex>

using namespace std;
typedef long long ll;

#define ALL(c) (c).begin(),(c).end()
#define FOR(i,l,r) for(int i=(int)l;i<(int)r;++i)
#define REP(i,n) FOR(i,0,n)
#define FORr(i,l,r) for(int i=(int)r-1;i>=(int)l;--i)
#define REPr(i,n) FORr(i,0,n)
#define EACH(i,c) for(__typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define IN(l,v,r) ((l)<=(v) && (v)<(r))
#define UNIQUE(v) v.erase(unique(ALL(v)),v.end())
//debug
#define DUMP(x)  cerr << #x << " = " << (x)
#define LINE()    cerr<< " (L" << __LINE__ << ")"

template<typename T,typename U> T pmod(T x,U M){return (x%M+M)%M;}

stringstream ss;

int main(){
	cin.tie(0); ios::sync_with_stdio(false);
	ss   <<fixed <<setprecision(20);
	cout <<fixed <<setprecision(20);

	int N,M,K;cin >> N >> M >> K;

	vector<map<int,vector<int>>> es(N);
	REP(i,M){
		int a,b,c;cin >> a >> b >> c;a--;b--;
		es[a][c].push_back(b);
		es[b][c].push_back(a);
	}
	vector<int> ds(K);REP(i,K)cin >>ds[i];

	vector<vector<bool> > dp(K+1,vector<bool>(N));
	REP(i,N)dp[0][i]=true;

	for(int k=1;k<=K;k++){
		REP(i,N)if(dp[k-1][i]){
			for(int n:es[i][ds[k-1]]){
				dp[k][n]=true;
			}
		}
	}

	vector<int> res;
	REP(i,N)if(dp[K][i])res.push_back(i);

	cout << res.size()<<endl;
	REP(i,res.size()){
		if(i!=0)cout <<" ";
		cout << res[i]+1;	
	}
	cout <<endl;
 	return 0;
 }