import Control.Monad
import Data.List
import qualified Data.Set as S

type YukiCity = ([City],[Road])
cities = fst
roads = snd
next rs c t = map (from c . fst) $ filter (\r -> link c (path r) && toll r == t) rs

type Road = (Path,Toll)
path = fst
toll = snd

type Path = (City,City)
link c (c1,c2) = c==c1 || c==c2
from c (c1,c2)
 | c == c1 = c2
 | c == c2 = c1

type Info = [Toll]
type City = Int
type Toll = Int

nub' = S.toList . S.fromList

main = do
 [n,m,k] <- map read . words <$> getLine
 abcs <- map (map read . words) <$> replicateM m getLine
 info <- map read . words <$> getLine
 let rs = map (\[a,b,c] -> ((a,b),c)) abcs
 let result = investigate ([1..n],rs) info
 print (length result)
 putStrLn (unwords (map show result))

investigate :: YukiCity -> Info -> [City]
investigate yc i = foldl' (move (roads yc)) (cities yc) i

move :: [Road] -> [City] -> Toll -> [City]
move rs cs t = nub' $ concatMap (\c -> next rs c t) cs