import sequtils,algorithm,strutils,intsets,tables,sugar
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()
let ABC = newSeqWith(m,(a:scan(),b:scan(),c:scan()))
var oks = newSeqWith(n+1,true)
k.times:
  var nexts = newSeqWith(n+1,false)
  let d = scan()
  for i in 0..<m:
    let abc = ABC[i]
    if abc.c != d: continue
    if oks[abc.a]: nexts[abc.b] = true
    if oks[abc.b]: nexts[abc.a] = true
  oks = nexts
let res = toSeq(1..n).filterIt(oks[it])
echo res.len
echo res.mapIt($it).join(" ")