Scanf.scanf "%s" (fun s ->
    let a = Array.make 10 0 in
    String.iter (fun c -> let n = int_of_char c - 48 in a.(n) <- a.(n) + 1) s;

    let rec loop i l =
        if i < 0 then l else
            if a.(i) > 0 then loop (i - 1) (i :: l)
                         else loop (i - 1) l
    in
    let show d1 d2 l =
        let digits = "0123456789" in
        let rec loop acc = function
            | [] -> acc
            | hd :: tl -> loop (String.make a.(hd) digits.[hd] ^ acc) tl
        in
        let acc = String.make (a.(d2) - 1) digits.[d2] ^
                  String.make 1            digits.[d1] ^
                  String.make 1            digits.[d2] ^
                  String.make (a.(d1) - 1) digits.[d1]
        in
        loop acc l
    in
    let l = loop 9 [] in
    match l with
    | []                        -> failwith "??"
    | [ _ ]                     -> print_endline "-1"
    | [ 0; d1 ] when a.(d1) = 1 -> print_endline "-1"
    | d1 :: d2 :: tl -> print_endline @@ show d1 d2 tl
)