let dig_of_char c = int_of_char c - int_of_char '0'
let char_of_dig d = char_of_int (d + int_of_char '0')

let solve s =
  let sarr = Array.make 10 0 in
  let slen = String.length s in

  let rec make_arr idx =
    if idx < slen then (
      let dig = dig_of_char s.[idx] in
      sarr.(dig) <- sarr.(dig) + 1;
      make_arr (idx + 1)
    )
  in
  make_arr 0;
  let rec solve' idx result =
    if idx < 0 then result
    else
      let s = String.make sarr.(idx) (char_of_dig idx) in
      solve' (idx - 1) (result ^ s)
  in
  solve' 9 ""

let () =
  let n = read_line () in
  solve n |> print_endline