exception Illegaalne of string;;

let kusi_arv (nimi, telg)
= try
    print_string ("Sisesta punkti " ^ nimi ^ " asukoht teljel " ^ telg ^ ": ");
    let sisu = read_line () in
    float_of_string sisu
  with
    | Failure (_) ->
            raise (Illegaalne (sisu));;