N, M, K = map(int, raw_input().strip().split())
E = [[] for i in range(N+1)]
for i in range(M):
    a, b, c = map(int, raw_input().strip().split())
    E[a].append((b, c))
    E[b].append((a, c))
ds = map(int, raw_input().strip().split())
ans = range(N+1)
while ds:
    ans = set(t for s in ans for (t, c) in E[s] if c == ds[0])
    ds = ds[1:]

L = len(ans)
print(L)
if L == 0:
    print(ans[0])
else:
    print(' '.join(map(str, ans)))