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

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

	int d, x, y;
	for (int i = 0; i < k; i++) {
		cin >> d;

		for (int j = 0; j < m; j++) {
			if (c[j] == d) {
				x = a[j];
				y = b[j];
				if (possible[i][x]) { possible[i + 1][y] = true; }
				if (possible[i][y]) { possible[i + 1][x] = 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;
}