import Control.Monad

main = do
  n <- readLn
  replicateM n $ do
         s <- getLine
         let
             f [] g = g == 0
             f (x:xs) g
               | x == 'W' = f xs g
               | x == 'G' = f xs (g+1)
               | g > 0 = f xs (g-1)
               | otherwise = False
          in putStrLn $ if length s < 3 || not (f s 0) then "impossible" else "possible"