N, M, K = map(int, input().split())
ABC = [list(map(int, input().split())) for _ in range(M)]
D = list(map(int, input().split()))
E = [{} for _ in range(N + 1)]
Q = set()
for a, b, c in ABC:
    if c not in E[a]:
        E[a][c] = [b]
    else:
        E[a][c].append(b)
    if c not in E[b]:
        E[b][c] = [a]
    else:
        E[b][c].append(a)
    if c == D[0]:
        Q.add(a)
        Q.add(b)
for i in range(K):
    Q2 = set()
    for q in Q:
        if D[i] in E[q]:
            for x in E[q][D[i]]:
                Q2.add(x)
    Q = Q2
print(len(Q))
print(*Q)