import sys
read=sys.stdin.buffer.read
readline=sys.stdin.buffer.readline

N,M,K=map(int,readline().split())
ABC=tuple(tuple(map(int,readline().split())) for _ in range(M))
D=tuple(map(int,read().split()))

p=[True]*(N+1)
for d in D:
  q=[False]*(N+1)
  for a,b,c in ABC:
    if c!=d: continue
    if p[a]: q[b]=True
    if p[b]: q[a]=True
  p=q
ans=[i for i, x in enumerate(p) if x]
print(len(ans))
print(*ans)