N,M,K=map(int,raw_input().split())
edge=[[]for i in range(N)]
s=set([])
for i in range(M):
    a,b,c = map(int,raw_input().split())
    edge[a-1].append((b-1,c))
    edge[b-1].append((a-1,c))
d=map(int,raw_input().split())
for i in range(N):
    for j,c in edge[i]:
        if c == d[0]:
            s.add(i)
for i in range(1,K):
    t=set([])
    for k in s:
        for j,c in edge[k]:
            if c==d[i]:
                t.add(j)
    s=t
ans=list(s)
ans.sort()
print len(ans)
for a in ans:
    print a+1,