let () =
  let a, b, x, y = Scanf.scanf "%d %d %d %d " (fun a b x y -> a, b, x, y) in
  let c = a + b in
  let s = float (x * c) /. (float a) in
  let t = float (y * c) /. (float b) in
  Printf.printf "%.7f\n" (if s <= float (x + y) then s else t)