#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <climits>
#include <cmath>
#include <string>
#include <vector>
#include <algorithm>
#include <queue>
#include <map>
#include <functional>
#include <set>
#include <numeric>
#include <stack>
#include <utility>
#include <time.h>
#include <iterator>
//#include "util.h"

using namespace std;
typedef unsigned uint;
typedef long long lint;
typedef unsigned long long ulint;



//呪文
template <typename _KTy, typename _Ty> ostream& operator << (ostream& ostr, const pair<_KTy, _Ty>& m) { cout << "{" << m.first << ", " << m.second << "}"; return ostr; }
template <typename _KTy, typename _Ty> ostream& operator << (ostream& ostr, const map<_KTy, _Ty>& m) { if (m.empty()) { cout << "{ }"; return ostr;	} cout << "{" << *m.begin(); for (auto itr = ++m.begin(); itr != m.end(); itr++) { cout << ", " << *itr; } cout << "}"; return ostr; }
template <typename _Ty> ostream& operator << (ostream& ostr, const vector<_Ty>& v) { if (v.empty()) { cout << "{ }"; return ostr; }	cout << "{" << v.front(); for (auto itr = ++v.begin(); itr != v.end(); itr++) { cout << ", " << *itr; }	cout << "}"; return ostr; }
template <typename _Ty> ostream& operator << (ostream& ostr, const set<_Ty>& s) { if (s.empty()) { cout << "{ }"; return ostr; } cout << "{" << *(s.begin()); for (auto itr = ++s.begin(); itr != s.end(); itr++) { cout << ", " << *itr; }	cout << "}"; return ostr; }
//template <typename T> void print(T* v, int N) { if (N == 0) cout << "{ }"; cout << "{" << v[0]; for (int i = 1; i < N; i++) cout << ", " << v[i]; cout << "}"; }
#define PI 3.14159265358979323846
#define EPS 1e-8
#define all(x) (x).begin(), (x).end()



typedef pair<int, int> pii;

int yuki0092()
{
	int N, M, K;
	cin >> N >> M >> K;

	// 隣接リスト (多重辺があるので隣接行列は適さない？)
	vector< vector<pii> > li(N + 1);

	int a, b, c;
	for (int i = 0; i < M; i++) {
		cin >> a >> b >> c;

		// (行き先, コスト)
		li[a].push_back(pii(b, c));
		li[b].push_back(pii(a, c));
	}

	vector<int> d(K);
	for (int i = 0; i < K; i++) cin >> d[i];

	// 考えられる行き先
	set<int> st;
	// 最初は全頂点を入れておく
	for (int i = 1; i <= N; i++) st.insert(i);

	for (int i = 0; i < K; i++) {
		set<int> tmp;

		for (auto itr = st.begin(); itr != st.end(); itr++) {
			for (int j = 0; j < li[*itr].size(); j++) {
				if (li[*itr][j].second == d[i]) {
					tmp.insert(li[*itr][j].first);
				}
			}
		}
		// この時点で tmp には d[i] までの情報を使って得られる
		// 犯人がいる可能性のある頂点が入っている

		st = tmp;
	}

	cout << st.size() << endl;
	
	cout << *(st.begin());
	for (auto itr = ++(st.begin()); itr != st.end(); itr++) {
		cout << " " << *itr;
	}
	cout << endl;

	return 0;
}

int main()
{
	//clock_t start, end;
	//start = clock();

	yuki0092();
	
	//end = clock();
	//printf("%d msec.\n", end - start);

	return 0;
}