N, M, K = map(int, input().split())

V = [[] for i in range(N)]

for i in range(M):
    a, b, c = map(int, input().split())
    V[a - 1] += [[b - 1, c]]
    
    V[b - 1] += [[a - 1, c]]
    
dp = [1] * N

for k in map(int, input().split()):
    dp1 = [0] * N
    
    for i in range(N):
        if dp[i]:
            for v, c in V[i]:
                if c == k:
                    dp1[v] = 1
    dp = dp1
    
print(sum(dp))
print(*(i + 1 for i in range(N) if dp[i]))