let solve aw ab bw bb c d =
  let cw1, cw2 =
    if ab >= c then (0, aw)
    else (c - ab, aw - (c - ab))
  in
  let dw = min (bw + cw1) d in
  cw2 + dw

let read_int_int () =
  read_line () |>
  Str.split (Str.regexp_string " ") |>
  List.map int_of_string |>
  fun lst -> (List.nth lst 0, List.nth lst 1)

let () =
  let aw, ab = read_int_int ()
  and bw, bb = read_int_int ()
  and c, d = read_int_int ()
  in
  solve aw ab bw bb c d |> string_of_int |> print_endline