exception Found of int

let pyramide n =
  try let carre = ref 0 in
      for i = 0 to (n + 1) / 2 do
        if n == !carre then raise (Found i);
        carre := !carre + 2 * i + 1
      done;
      -1
  with Found m -> 2 * m - 1

let _ =
  let n = read_int () in
  print_int (pyramide n);
  print_newline ()