N,M,K = map(int,input().split())
L = [[] for _ in range(N+1)] 
for i in range(M):
    a,b,c = map(int,input().split())
    L[a].append((b,c))
    L[b].append((a,c))
D = list(map(int,input().split()))[::-1]
ANS = []
for i in range(1,N+1):
    S = set()
    S.add(i)
    for d in D:
        NEXT = set()
        for s in S:
            for l in L[s]:
                n,c = l
                if d==c:
                    NEXT.add(n)
        S = NEXT
    if len(S):
        ANS.append(i)
print(len(ANS))
print(*ANS)