let () =
    let arr = Array.make 4 0 in
    Scanf.scanf "%d %d\n" (fun x y -> arr.(0) <- x; arr.(1) <- y);
    Scanf.scanf "%d %d\n" (fun x y -> arr.(2) <- x; arr.(3) <- y);

    Array.map float_of_int arr |>
    fun arr -> abs_float (arr.(2) -. arr.(0)) /. 2. +. abs_float (arr.(3) -. arr.(1)) /. 2. |>
    Printf.printf "%f"