#include <iostream>
#include <cstdio>
#include <vector>
#include <algorithm>
#include <utility>
#include <string>
#include <set>

using namespace std;

int main() {
	int n, m, k;

	cin >> n >> m >> k;
	vector< vector< set<int> > > price(n + 1, vector< set<int> >(n + 1));

	int a, b, c;
	for (int i = 0; i < m; i++) {
		cin >> a >> b >> c;
		price[a][b].insert(c);
		price[b][a].insert(c);
	}

	vector< vector<bool> > possible(k + 1, vector<bool>(n + 1, false));
	fill(possible[0].begin() + 1, possible[0].end(), true);

	int d;
	for (int i = 0; i < k; i++) {
		cin >> d;
		for (int j = 0; j <= n; j++) {
			if (!possible[i][j]) {
				continue;
			}

			for (int h = 1; h <= n; h++) {
				if (price[j][h].count(d) > 0) {
					possible[i + 1][h] = true;
				}
			}
		}
	}

	vector<int> ans;
	for (int i = 0; i <= n; i++) {
		if (possible[k][i]) {
			ans.push_back(i);
		}
	}
	cout << ans.size() << endl;
	for (int i = 0; i < ans.size(); i++) {
		if (i != 0) {
			cout << " ";
		}
		cout << ans[i];
	}
	cout << endl;

	return 0;
}