let code_a = int_of_char 'a'
let char_of_i i = char_of_int (code_a + i)

let n = Scanf.sscanf (read_line ()) "%d" @@ fun n -> n

let rec f acc n =
  let acc = (char_of_i ((n - 1) mod 26)) :: acc in
  if n <= 26 then acc |> List.map Char.escaped |> String.concat "" |> print_endline
  else f acc (n / 26)

let () = f [] n