let () = Scanf.scanf "%d\n" @@ fun n ->
  let vs = Array.init n @@ fun _ -> Scanf.scanf "%d " @@ fun v -> v in
  Array.sort compare vs;
  Printf.printf "%.9f\n" @@
  Array.fold_left (fun s v -> (s +. float_of_int v) *. 0.5) (float_of_int vs.(0)) vs

