let make_list f t step =
  let rec make_list_inner c t lst =
    if c >= t then lst else make_list_inner (c+step) t (c::lst)
  in
  List.rev (make_list_inner f t [])

let print_list str list = Printf.printf "%s: [ " str; List.iter (fun (q,r) -> Printf.printf "(%d, %d); " q r) list; Printf.printf "]\n"

let () =
  let rec read lst =
    try let ans = read_line () in
        read (ans::lst)
    with End_of_file ->
      let lst = List.sort (compare) lst in
      Printf.printf "%s\n" (List.fold_left (^) "" lst)
  in
  ignore (read_line ());
  read []
;;
