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 need_amedama a b c = a * (b - c);;
let rec buy_amedama pay need i d e =
  match need with
  | 0 -> pay
  | _ ->
    let need = need - 1 in
    let i = i + 1 in
    let d = if ((i mod 10) = 0 && (d >= e)) then (d - e) else d in
    let pay = pay + d in
    buy_amedama pay need i d e;;

let () =
  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
  let c = List.nth raw 2 in
  let need = need_amedama a b c in
  let d = List.nth raw 3 in
  let e = List.nth raw 4 in
  buy_amedama 0 need 0 d e |> print_int; print_newline ();;