import Control.Applicative
import Control.Monad
import Data.Bool (bool)

main :: IO ()
main = do
  n <- readLn
  map solve <$> replicateM n getLine >>= mapM_ putStrLn

solve :: String -> String
solve bs = bool "impossible" "possible" $ last bs == 'R' && last (filter (/= 'R') bs) == 'G' && f (0, 0) bs
  where
    f (_, g) [] = g == 0
    f (w, g) (b:bs)
      | b == 'R' = if g > 0
                     then f (w, g - 1) bs
                     else False
      | b == 'G' = if w > 0
                     then f (w - 1, g + 1) bs
                     else False
      | otherwise = f (w + 1, g) bs