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' && f 0 bs
  where
    f g [] = g == 0
    f g (b:bs)
      | b == 'R' = if g > 0
                     then f (g - 1) bs
                     else False
      | b == 'G' = f (g + 1) bs
      | otherwise = f g bs