open Printf
open Scanf

let () =
  let n = scanf " %d" (fun x -> x) in
  let a = Array.init n (fun _ -> scanf " %f" (fun x -> x)) |> Array.to_list |> List.sort compare in
  List.fold_left (fun x y -> (x +. y) /. 2.0) (List.hd a) (List.tl a)
  |> printf "%.15f\n"