#coding: utf-8
#yuki_92

n,m,k=map(int,raw_input().split())
edge=[[] for i in xrange(n)]
s=set([])
for i in xrange(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 xrange(n):
 for j,c in edge[i]:
  if c==d[0]:
   s.add(i)
   
for i in xrange(1,k):
 t=set([])
 for k in s:
  for j,c in edge[k]:
    if c==d[i]:
     t.add(j)
 s=t
 
res=list(s)
print len(res)
res.sort()
for i in res:
 print i+1,