let (h, w) = Scanf.scanf "%d %d\n" (fun h w -> (h, w))
let (a, b) = Scanf.scanf "%d %d\n" (fun a b -> (a, b))
let (u, v) = ((h / a) * a, (w / b) * b)
let area = h * w - u * v
let () = Printf.printf "%d\n" area

