N,M,K=map(int,input().split())
E=[tuple(map(int,input().split())) for i in range(M)]
D=list(map(int,input().split()))

Q=set(range(1,N+1))

for d in D:
    NQ=set()

    for a,b,c in E:
        if c==d and a in Q:
            NQ.add(b)
        if c==d and b in Q:
            NQ.add(a)

    Q=NQ

print(len(Q))
print(*sorted(Q))