#include "bits/stdc++.h"

using namespace std;
using ll = long long;
const double pi = acos(-1);
#define FOR(i,a,b) for (ll i=(a),__last_##i=(b);i<__last_##i;i++)
#define RFOR(i,a,b) for (ll i=(b)-1,__last_##i=(a);i>=__last_##i;i--)
#define REP(i,n) FOR(i,0,n)
#define RREP(i,n) RFOR(i,0,n)
#define __GET_MACRO3(_1, _2, _3, NAME, ...) NAME
#define rep(...) __GET_MACRO3(__VA_ARGS__, FOR, REP)(__VA_ARGS__)
#define rrep(...) __GET_MACRO3(__VA_ARGS__, RFOR, RREP)(__VA_ARGS__)
template<typename T> ostream& operator<<(ostream& os, const vector<T>& v) {
	REP(i, v.size()) { if (i)os << " "; os << v[i]; }return os;
}
template<typename T> ostream& operator<<(ostream& os, const vector<vector<T>>& v) {
	REP(i, v.size()) { if (i)os << endl; os << v[i]; }return os;
}

const ll INF = LLONG_MAX;
ll MOD = 1000000007;
ll _MOD = 1000000009;
double EPS = 1e-10;

#define int long long

inline void my_io() {

	std::ios::sync_with_stdio(false);

	std::cin.tie(0);

	cout << fixed << setprecision(16);

	//cout << setprecision(10) << scientific << ans << endl;
}

signed main() {
	ll n, m, k, a, b, c, d;

	cin >> n >> m >> k;

	vector<vector<pair<ll, ll>>> G(n);

	REP(i, m) {
		cin >> a >> b >> c;
		G[a - 1].push_back(make_pair(b - 1, c));
		G[b - 1].push_back(make_pair(a - 1, c));
	}

	vector<bool> ans(n, true);

	REP(i, k) {
		cin >> d;

		vector<bool> v(n, false);

		REP(j, n) {
			if (!ans[j]) continue;

			REP(t, G[j].size()) {
				if (G[j][t].second == d) {
					v[G[j][t].first] = true;
				}
			}
		}

		ans = v;
	}

	vector<ll> ans2;

	REP(i, n) {
		if (ans[i]) {
			ans2.push_back(i + 1);
		}
	}

	cout << ans2.size() << endl;
	cout << ans2 << endl;
}