let listing n =
    let rec loop acc i =
        if i <= n then loop (i::acc) (i + 1) else List.rev acc in
    loop [] 1

let _ =
    let n = Scanf.scanf "%d\n" (fun n -> n) in
    Printf.printf "%d\n"
    @@ List.fold_left (fun x y -> x + y) 0 (listing n)

