from collections import defaultdict
N, M, K = map(int, input().split())

cost = [defaultdict(list) for _ in range(N)]

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

D = list(map(int, input().split()))
ans = set()
for i in range(N): # 出発点
    positions = {i}
    next_positions = set()

    for j in range(K):

        for pos in positions:
            # pos から D[j] のコストで行ける場所
            for nex in cost[pos][D[j]]:
                next_positions.add(nex)
        
        positions = next_positions
        next_positions = set()

    # K回の移動後になお、positionsにいる頂点が答え

    for pos in positions:
        ans.add(pos + 1)

ans2 = sorted(ans)
print(len(ans2))
print(*ans2)