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

proc putchar_unlocked(c:char){. importc:"putchar_unlocked",header: "<stdio.h>" .}
proc printInt(a:int32) =
  if a == 0:
    putchar_unlocked('0')
    return
  template div10(a:int32) : int32 = cast[int32]((0x1999999A * cast[int64](a)) shr 32)
  template mod10(a:int32) : int32 = a - (a.div10 * 10)
  var n = a
  var rev = a
  var cnt = 0
  while rev.mod10 == 0:
    cnt += 1
    rev = rev.div10
  rev = 0
  while n != 0:
    rev = rev * 10 + n.mod10
    n = n.div10
  while rev != 0:
    putchar_unlocked((rev.mod10 + '0'.ord).chr)
    rev = rev.div10
  while cnt != 0:
    putchar_unlocked('0')
    cnt -= 1
proc printInt(a:int,last:char) =
  a.int32.printInt()
  putchar_unlocked(last)





let n = scan()
let m = scan()
let k = scan()
var P = newTable[int,seq[tuple[a,b:int]]]()
m.times:
  let a = scan()
  let b = scan()
  let c = scan()
  if c notin P : P[c] = @[]
  P[c] &= (a,b)
let D = newSeqWith(k,scan())
var nows = initIntSet()
for p in P[D[0]]:
  nows.incl p.a
  nows.incl p.b
for i in 1..<k:
  var nexts = initIntSet()
  for p in P[D[i]]:
    if p.a in nows:
      nexts.incl p.b
    if p.b in nows:
      nexts.incl p.a
  nows = nexts
printInt(nows.card,'\n')
for x in toSeq(nows.items).sorted(cmp):
  printInt(x,' ')
putchar_unlocked('\n')