from collections import defaultdict

N,M,K=map(int,input().split())
E=defaultdict(list)
for _ in range(M):
    a,b,c=map(int,input().split())
    E[c].append((a,b))
D=map(int,input().split())

S=set(range(1,N+1))
for d in D:
    T=set()
    for u,v in E[d]:
        if u in S:
            T.add(v)
        if v in S:
            T.add(u)
    S=T.copy()

print(len(S))
print(*sorted(S))