def tousou(N, M, K, abcs, ds):
    abs = []
    cs = []
    for i in range(M):
        abc = abcs[i]
        abs.append([abc[0], abc[1]])
        cs.append(abc[2])
    koho = []
    for j in range(M):
        if cs[j] == ds[0]:
            koho.append(abs[j][0])
            koho.append(abs[j][1])
    koho = list(set(koho))
    for k in range(1, K):
        d = ds[k]
        koho2 = []
        for l in range(M):
            if cs[l] == d:
                ab = abs[l]
                if ab[0] in koho:
                    koho2.append(ab[1])
                if ab[1] in koho:
                    koho2.append(ab[0])
        koho = list(set(koho2))
    ans1 = len(koho)
    koho = sorted(koho)
    map_koho = list(map(str, koho))
    ans2 = ' '.join(map_koho)
    return [ans1, ans2]

def main():
    N, M, K = map(int, input().split())
    abcs = [0 for x in range(M)]
    for i in  range(M):
        abcs[i] = list(map(int, input().split()))
    ds = list(map(int, input().split()))
    ans = tousou(N, M, K, abcs, ds)
    print(ans[0])
    print(ans[1])

if __name__ == '__main__':
    main()