from collections import defaultdict

N,M,K = [int(i) for i in input().split()]
G = [defaultdict(set) for i in range(N)]

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

candidates = set(range(N))
for k in map(int, input().split()):
    new_candidates = set([])
    for i in candidates:
        if k in G[i]:
            new_candidates |= G[i][k]
    candidates = new_candidates

print(len(candidates))
print(" ".join([str(i+1) for i in candidates]))