n, m, k = map(int, input().split())
edges = [[] for _ in range(n)]
for _ in range(m):
    a, b, c = map(int, input().split())
    a -= 1
    b -= 1
    edges[a].append((b, c))
    edges[b].append((a, c))
D = list(map(int, input().split()))
se = set(range(n))
for d in D:
    se2 = set()
    for pos in se:
        for npos, c in edges[pos]:
            if c == d:
                se2.add(npos)
    se = se2
    
print(len(se))
lst = sorted(se)
print(*(l + 1 for l in lst))