N, M, K = map(int, input().split())
G = [[] for _ in range(N + 1)]
for _ in range(M):
	a, b, c = map(int, input().split())
	G[a].append((b, c))
	G[b].append((a, c))
d = list(map(int, input().split()))

kouho = set(range(1, N + 1))
for i in range(K):
	new_kouho = set()
	for j in kouho:
		for (v, c) in G[j]:
			if c == d[i]:
				new_kouho.add(v)
	kouho = new_kouho

print(len(kouho))
print(' '.join(map(str, kouho)))