N, M, K = map(int, input().split())
ABC = tuple(tuple(map(int, input().split())) for _ in range(M))
D = tuple(map(int, input().split()))
dp = [[False] * (N+1) for _ in range(K+1)]
for i in range(N+1):
    dp[0][i] = True
for i in range(K):
    for j in range(M):
        if D[i] == ABC[j][2]:
            if dp[i][ABC[j][0]]:
                dp[i+1][ABC[j][1]] = True
            if dp[i][ABC[j][1]]:
                dp[i+1][ABC[j][0]] = True
print(dp[K].count(True))
a = [i for i in range(N+1) if dp[K][i]]
print(*a)