import sequtils,algorithm,strutils,intsets,tables
template times*(n:int,body) = (for _ in 0..<n: body)

proc getchar_unlocked():char {. importc:"getchar_unlocked",header: "<stdio.h>" .}
proc scan(): int =
  while true:
    let k = getchar_unlocked()
    if k < '0': break
    result = 10 * result + k.ord - '0'.ord


let n = scan()
let m = scan()
let k = scan()
# var oks = initIntSet()
# for i in 1..n: oks.incl i
# var P = newSeqWith(n+1,newSeqWith(n+1,newSeq[int]()))
# m.times:
#   let a = scan()
#   let b = scan()
#   let c = scan()
#   P[a][b] &= c
#   P[b][a] &= c
# var nexts = initIntSet()
# k.times:
#   let d = scan()
#   for ok in oks:
#     for p in P[ok]:
#       for pi in p:
#         if d notin pi: continue
#         nexts.incl d
#   oks = nexts
# echo oks
const INF = 10003
proc hash(n:int) : int = n mod INF

var P = newSeq[seq[tuple[a,b:int]]](INF)
m.times:
  let a = scan()
  let b = scan()
  let c = scan()
  if P[c.hash].len == 0 : P[c.hash] = @[]
  P[c.hash] &= (a,b)
let D = newSeqWith(k,scan())
var answers = initIntSet()
for p in P[D[0].hash]:
  answers.incl p.a
  answers.incl p.b
for i in 1..<k:
  var nexts = initIntSet()
  for p in P[D[i].hash]:
    if p.a in answers:
      nexts.incl p.b
    if p.b in answers:
      nexts.incl p.a
  answers = nexts
echo answers.card
echo toSeq(answers.items).sorted(cmp).mapIt($it).join(" ")