#include "bits/stdc++.h"

using namespace std;

using ll = long long int;
using ld = long double;

using pii = pair<int, int>;
using pll = pair<ll, ll>;
using pdd = pair<double, double>;
using vi = vector<int>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vl = vector<ll>;
using vvl = vector<vl>;
using vvvl = vector<vvl>;
using vd = vector<double>;
using vvd = vector<vd>;
using vs = vector<string>;
using vb = vector<bool>;
using vvb = vector<vb>;

const int INF = (1 << 30) - 1;
const ll INF64 = ((ll)1 << 62) - 1;
const double PI = 3.1415926535897932384626433832795;

const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { -1, 0, 1, 0 };

int gcd(int x, int y) { return y ? gcd(y, x % y) : x; }
ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : x; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	int n, m, k;
	cin >> n >> m >> k;

	vector<map<int, vi>> gold(n);
	for (int i = 0; i < m; i++) {
		int a, b, c;
		cin >> a >> b >> c;
		a--; b--;

		gold[a][c].push_back(b);
		gold[b][c].push_back(a);
	}

	vi ds(k);
	for (int i = 0; i < k; i++) cin >> ds[i];

	set<int> xs;
	for (int i = 0; i < n; i++) xs.insert(i);

	for (auto d : ds) {
		set<int> ys;
		for (auto x: xs) {
			if (gold[x].count(d)) {
				for (auto y : gold[x][d]) {
					ys.insert(y);
				}
			}
		}
		xs = ys;
	}

	cout << xs.size() << endl;
	for (auto x : xs) cout << x + 1 << " ";
	cout << endl;
	return 0;
}