let split_on_char sep s =
  let r = ref [] in
  let j = ref (String.length s) in
  for i = String.length s - 1 downto 0 do
    if String.unsafe_get s i = sep then begin
      r := String.sub s (i + 1) (!j - i - 1) :: !r;
      j := i
    end
  done;
  String.sub s 0 !j :: !r;;

let party_hard x a b d = (x * a) + ((d - x) * b);;

let party_open a b d =
  let rec lets_party min_cost x =
    match x with
    | (-1) -> min_cost
    | _ ->
      let now_cost = party_hard x a b d in
      lets_party (min min_cost now_cost) (x - 1)
  in
  lets_party (max_int) d;;

let () =
  let d = read_line () |> int_of_string in
  let raw = read_line () |> split_on_char ' ' |>
            List.map int_of_string in
  let a = List.nth raw 0 in
  let b = List.nth raw 1 in
  party_open a b d |> print_int;
  print_newline ();;