N, M, K = map(int, input().split())
A = [0] * M
B = [0] * M
C = [0] * M
dp = [[0 for _ in range(1010)] for _ in range(110)]

for i in range(M):
    a, b, c = map(int, input().split())
    A[i] = a
    B[i] = b
    C[i] = c

D = list(map(int, input().split()))

for i in range(M):
    if D[0] == C[i]:
        dp[0][A[i]] = 1
        dp[0][B[i]] = 1

for i in range(1, K):
    for j in range(M):
        if D[i] == C[j]:
            if dp[i - 1][A[j]]:
                dp[i][B[j]] = 1
            if dp[i - 1][B[j]]:
                dp[i][A[j]] = 1

t = 0
for i in range(101):
    t += sum(dp[K - 1 + i])
print(t)

pos = []
for i in range(101):
    if dp[K - 1][i]:
        pos.append(str(i))

print(" ".join(pos))