#include <iostream>
using namespace std;

int a[1000], b[1000], c[1000], d[1000];
bool pos[1001][101];
// pos[k][i] := k 回目の移動後に町 i にいる可能性

int main() {
	int N, M, K;
	cin >> N >> M >> K;
	for (int j = 0; j < M; j++)
		cin >> a[j] >> b[j] >> c[j];
	for (int k = 0; k < K; k++)
		cin >> d[k];

	fill(pos[0] + 1, pos[0] + N, true);
	for (int k = 0; k < K; k++)
		for (int j = 0; j < M; j++)
			if (c[j] == d[k]) {
				int u = a[j], v = b[j];
				if (pos[k][u])
					pos[k + 1][v] = true;
				if (pos[k][v])
					pos[k + 1][u] = true;
			}

	int cnt = 0;
	for (int i = 1; i <= N; i++)
		if (pos[K][i])
			cnt++;
	cout << cnt << endl;
	for (int i = 1; i <= N; i++)
		if (pos[K][i])
			cout << i << ' ';
	cout << endl;
}