import Control.Monad
solve _ _ [] = "possible"
solve w g (c:cs) = case c of 
  'W' | w /= 0 -> solve w g cs
  'G' | w /= 0 -> solve (w-1) (g+1) cs
  'R' | g /= 0 -> solve w (g-1) cs
  _ -> "impossible"
main = do
  t <- readLn
  ss <- replicateM t getLine
  mapM_ (putStrLn . solve 3 0) ss