let () =
  let rec loop () = match read_int () with
      0 -> ()
    | n ->
      let nums = Str.split (Str.regexp " ") (read_line ())
                 |> List.map float_of_string  in
      let average =  (List.fold_left (+.) 0. nums) /. (float n) in
      let v = (List.fold_left (fun acc s -> acc +. (s -. average) ** 2. ) 0. nums) /. (float n) in
      let sd = sqrt v in
      Printf.printf "%f\n" sd;
      loop ()
  in loop ()