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

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

  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 $ [x+1..n-1] ++ (reverse [1..x-1]) ++ [x]
