import sys
input = sys.stdin.readline
sys.setrecursionlimit(10**8)

def dfs(cn, depth):
    if depth == K:
        return [cn]
        
    res  = []
    
    for nn, w in adj_list[cn]:
        if d[depth] == w:
            res += dfs(nn, depth+1)
    
    return res

N, M, K = map(int, input().split())
adj_list = [[] for _ in range(N)]

for _ in range(M):
    a, b, c = map(int, input().split())
    adj_list[a-1].append((b-1, c))
    adj_list[b-1].append((a-1, c))

d = list(map(int, input().split()))
ans = set()

for i in range(N):
    ans |= set(dfs(i, 0))

ans = list(sorted(map(lambda x: x+1, list(ans))))

print(len(ans))
print(*ans)