open System

let ri () = stdin.ReadLine() |> int
let ria () = stdin.ReadLine().Split() |> Array.map int

type Sol() =
    member this.Solve() = 
        let [|N;M|] = ria()
        let [|X;Y|] = ria()
        
        let f m a =
            let x = a % (2*m)
            if x < m then (x+1) else ( 2*m - x )
        
        //f M (X-1) |> printfn "%d"
        //f M (Y-1) |> printfn "%d"
        
        let jdg a b = (f M (a-1)) = (f M (b-1)) 
        
        (if jdg X Y then "YES" else "NO" ) |> printfn "%s"
        
        
        
        ()
let mySol = new Sol()
mySol.Solve()