let n = stdin.ReadLine() |> float

let rate = 1.08

let ans =
  let x = n / rate |> ceil
  [ let mutable y = x
    while y < (n + 1.) / rate do
      yield y
      y <- y + 1. ]
  |> (fun l ->
        match l with
        | [] -> ":("
        | x :: _ -> sprintf "%d" (int x))

ans |> stdout.WriteLine