n, m, k = map(int, input().split())

G = [[] for _ in range(n+1)]

for i in range(m):
    a, b, c = map(int, input().split())
    G[a].append((b, c))
    G[b].append((a, c))
    
d = list(map(int, input().split()))

visit = set(range(1, n+1))
for i in range(k):
    tmp = set()
    for j in visit:
        for (v, c) in G[j]:
            if c == d[i]:
                tmp.add(v)
    visit = tmp

print(len(visit))
print(" ".join(map(str, visit)))