## https://yukicoder.me/problems/no/92

def main():
    N, M, K = map(int, input().split())
    money_map = {}
    for _ in range(M):
        a, b, c = map(int, input().split())
        if c not in money_map:
            money_map[c] = []
        money_map[c].append((a - 1, b - 1))
        money_map[c].append((b - 1, a - 1))
    D = list(map(int, input().split()))

    array = [True] * N
    for d in D:
        new_array = [False] * N

        for a, b in money_map[d]:
            new_array[b] |= array[a]
        array = new_array

    answer = []    
    for i in range(N):
        if array[i]:
            answer.append(str(i + 1))
    print(len(answer))
    print(' '.join(answer))

    






if __name__ == '__main__':
    main()