#include <iostream>
#include <vector>

using namespace std;

int main() {
	int n, m, k;
	cin >> n >> m >> k;
	vector<int> a(m), b(m), c(m);
	for (int i = 0; i < m; ++i) {
		cin >> a[i] >> b[i] >> c[i];
	}
	vector<int> d(k);
	for (int i = 0; i < k; ++i) {
		cin >> d[i];
	}
	static bool exists[101][1000] = { false }; // [city][log]
	for (int i = 0; i < m; ++i) {
		bool e = (c[i] == d[0]);
		exists[a[i]][0] |= e;
		exists[b[i]][0] |= e;
	}
	for (int j = 1; j < k; ++j) {
		for (int i = 0; i < m; ++i) {
			if (exists[a[i]][j - 1]) {
				bool e = (c[i] == d[j]);
				exists[b[i]][j] |= e;
			}
			if (exists[b[i]][j - 1]) {
				bool e = (c[i] == d[j]);
				exists[a[i]][j] |= e;
			}
		}
	}
	vector<int> cityNumbers;
	for (int i = 1; i <= n; ++i) {
		if (exists[i][k - 1]) {
			cityNumbers.push_back(i);
		}
	}
	cout << cityNumbers.size() << endl;
	for (size_t i = 0; i < cityNumbers.size(); ++i) {
		if (i > 0) {
			cout << " ";
		}
		cout << cityNumbers[i];
	}
	cout << endl;
	return 0;
}