module String = struct
  include String

  (* @since 4.02.0 *)
  let mapi f s =
    let l = Bytes.length s in
    if l = 0 then s else begin
      let r = Bytes.create l in
      for i = 0 to l - 1 do Bytes.set r i (f i s.[i]) done;
      r
    end

end

let () =
  read_line ()
  |> String.mapi (fun i c ->
    (Char.code c - Char.code 'A' - ((i + 1) mod 26) + 26) mod 26 + Char.code 'A' |> Char.chr)
  |> print_endline