from collections import defaultdict

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

for _ in range(M):
    a, b, c = map(int, input().split())
    dic[c].add((a, b))

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

ans = set()
for n in d[:1]:
    for j in dic[n]:
        ans.add(j[0])
        ans.add(j[1])

for fee in d[1:]:
    m = set()
    for path in dic[fee]:
        ra, rb = path
        if ra in ans:
            m.add(rb)
        if rb in ans:
            m.add(ra)
    ans = m

print(len(ans))
print(' '.join(map(str, list(ans))))