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

D = list(map(int, input().split()))

pre = [1] * N
for i in range(K):
    dp = [0] * N
    for s in range(N):
        if not pre[s]:
            continue
        for u, c in G[s]:
            if c != D[i]:
                continue
            dp[u] |= pre[s]
    dp, pre = pre, dp

ans = []
for i in range(N):
    if pre[i]:
        ans.append(i + 1)

print(len(ans))
print(*ans)