let array_dim_2 h w =
  let ret = Array.make w [||] in
  for i = 0 to (w-1) do
    ret.(i) <- Array.make h 0
  done;
  ret

let solve h w a b =
  let dp = array_dim_2 h w in
  for x = 0 to (w-1) do
    dp.(x).(0) <- 1
  done;
  for y = 0 to (h-1) do
    dp.(0).(y) <- 1
  done;
  for x = 1 to (w-1) do
    for y = 1 to (h-1) do
      dp.(x).(y) <-
        if x > (w-b) || y < (h-a) then
          dp.(x-1).(y) + dp.(x).(y-1)
        else
          0
    done
  done;
  dp.(w-1).(h-1)



let () =
  let h, w, a, b = Scanf.scanf "%d %d %d %d\n" (fun w x y z -> w, x, y, z) in
  let ans = solve h w a b in
  Printf.printf "%d\n" ans
;;
