N, M, K = map(int, input().split())
adj = [[] for i in range(N)]
for i in range(M):
    a, b, c = map(int, input().split())
    a -= 1
    b -= 1
    adj[a].append((b, c))
    adj[b].append((a, c))
D = list(map(int, input().split()))[::-1]
ans = []
for end in range(N):
    prev = set([end])
    for i in range(K):
        nex = set()
        for p in prev:
            for nv, c in adj[p]:
                if c == D[i]:
                    nex.add(nv)
        prev = nex
    if len(prev) > 0:
        ans.append(end + 1)
print(len(ans))
print(*ans)