let () = Scanf.scanf "%d %d\n" @@ fun n l ->
  let a =
    Array.init n @@ fun _ ->
      Scanf.scanf "%d " @@ fun a -> a in
  try
    Array.init (n - 1) (fun i -> i)
    |> Array.to_list
    |> List.find (fun i -> l <= a.(i) + a.(i + 1))
    |> fun k ->
        print_endline "Possible";
        for i = 0 to k - 1 do
          Printf.printf "%d\n" @@ i + 1
        done;
        for i = n - 2 downto k do
          Printf.printf "%d\n" @@ i + 1
        done
  with Not_found -> print_endline "Impossible"