n, m, k = map(int,input().split())
A = []
B = []
C = []
for i in range(m):
    a, b, c = map(int,input().split())
    A.append(a-1)
    B.append(b-1)
    C.append(c)
D = list(map(int,input().split()))

dp = [[0]*n for _ in range(k)]
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]:
            dp[i][A[j]] |= dp[i-1][B[j]]
            dp[i][B[j]] |= dp[i-1][A[j]]
           
print(sum(dp[k-1]))
ans = []
for i in range(n):
    if dp[k-1][i]:
        ans.append(i+1)
print(*ans)