#define _USE_MATH_DEFINES

#include <iostream>
#include <iomanip>

#include <algorithm>
#include <cmath>

#include <string>
#include <list>
#include <queue>
#include <vector>
#include <complex>
#include <set>

/////////
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define P(p) cout<<(p)<<endl;
/////////
typedef long long LL;
typedef long double LD;
/////////
using namespace::std;
/////////
int A[1000];
int B[1000];
int C[1000];
int D[1000];

int main(void){
    std::cin.tie(0);
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed;//
    //cout << setprecision(6);//
	
	int N,M,K;
	cin>>N>>M>>K;

	rep(i,M){
		cin>>A[i]>>B[i]>>C[i];
	}
	rep(i,K){
		cin>>D[i];
	}
	/////
	set<int> now,next;
	
	{
		for(int i=0;i<M;++i){
			if(C[i] == D[0]){
				now.insert(A[i]);
				now.insert(B[i]);
			}
		}
	}

	for(int k=1;k<K;++k)
	{
		for(int i=0; i<M; ++i){
			if(C[i] == D[k]){
				if( now.find(A[i]) != now.end() ){
					//見つかった
					next.insert(B[i]);
				}
				if( now.find(B[i]) != now.end() ){
					//見つかった
					next.insert(A[i]);
				}
			}
		}
		//////
		now.clear();
		now.swap(next);
	}
	//sort(now.begin(),now.end());
	cout << now.size() << endl;
	set<int>::iterator itr = now.begin();
	while(itr != now.end()){
		cout << *itr;
		++itr;
		if( itr != now.end() ){
			cout << " ";
		}
	}
	cout << endl;
	return 0;
}