N, M, K = map(int,input().split())

l = [[] for i in range(N)]
ans_l = []

def find_s(node, times):
    global ans_l
    if times == len(pay_l):
        ans_l.append(node)
        return 0 
    for li in l[node]:
        if li[0] == pay_l[times]:
            find_s(li[1],times + 1) 


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

pay_l = list(map(int, input().split()))


for i in range(N):
    for l_i in l[i]:
        if l_i[0] == pay_l[0]:
            find_s(l_i[1], 1)


print(len(ans_l))
moji = ""
for li in ans_l:
    moji += str(li + 1) + " "
print(moji)