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())


def dfs(s, lst):
    if not lst:
        return [s]
    return [x
            for (t, c) in E[s] if c == lst[0]
            for x in dfs(t, lst[1:])]

ss = set(s for i in range(N+1) for (s, c) in E[i] if c == ds[0])
ans = sorted(set(z for s in ss for z in dfs(s, ds[1:])))
L = len(ans)
print(L)
if L == 0:
    print(ans[0])
else:
    print(' '.join(map(str, ans)))