let doIt () =
    let N, M = stdin.ReadLine () |> fun line -> line.Split () |> fun arr -> (int arr.[0], int arr.[1])
    let X, Y = stdin.ReadLine () |> fun line -> line.Split () |> fun arr -> (int arr.[0], int arr.[1])

    let getClass num =
        let n1, n2 = (num - 1) % M, ((num - 1) / M) % 2
        if n2 = 0 then n1 else M - n1 - 1

    let c1, c2 = getClass X, getClass Y

    c1 = c2 |> (function | true -> "YES" | false -> "NO") |> printfn "%s"

doIt ()