import Control.Applicative
import Control.Monad
import Data.List

check :: String -> String
check str = if check_sub 0 True 0 str then "possible" else "impossible"
  where
    check_sub w t g ""                   = t && g == 0
    check_sub w t g ('W':xs)             = check_sub (w+1) False  g    xs
    check_sub w t g ('G':xs) | w > 0     = check_sub (w-1) True  (g+1) xs
                             | otherwise = False
    check_sub w t g ('R':xs) | g > 0     = check_sub  w    t     (g-1) xs
                             | otherwise = False

main = do
  mapM_ putStrLn =<< map check <$> drop 1 <$> lines <$> getContents