import sys
input = sys.stdin.readline

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()))
dp = [[False] * N for _ in range(K+1)]
dp[0] = [True] * N

for i in range(K):
    for j in range(N):
        for k, w in adj_list[j]:
            if d[i] == w:
                dp[i+1][j] |= dp[i][k]

ans = [i+1 for i in range(N) if dp[K][i]]

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