import Control.Applicative
import Data.Array.Unboxed
import Data.Maybe
import Data.List
import Data.Int

main = do
  [n,l] <- map read . words <$> getLine :: IO [Int64]
  as <- listArray (1,n) . map read . words <$> getLine :: IO (UArray Int64 Int64)

  let ans = find (\i -> as!i + as!(i+1) >= l) [1..n-1]

  case ans of
    Nothing -> putStrLn "Impossible"
    Just x -> do
      putStrLn "Possible"
      mapM_ print $ [1..x-1] ++ (reverse [x..n-1])
