let split = Str.split (Str.regexp_string " ");;

let rec read () =
  let n = read_float () in
  if n != 0. then
    let l = read_line () |> split |> List.map float_of_string in
    let avg = (List.fold_left (+.) 0. l)/.n in
    (List.fold_left (fun x y -> x +. (y-.avg)**2.) 0. l)/.n
    |> sqrt |> Printf.printf "%.8f\n";read ();;

let () = read ();;