// ----   /￣￣￣￣￣￣￣/
//-+--+- /  maybe AC. /
// |  | ∠____________/

let f n x a b =
    let minOverFlow = pown 2 (n - 1)
    let zero        = 0    
    let calStep diff y =
        match diff % y with
        | 0 -> diff / y
        | _ -> diff / y + 1    
    let attackStep = calStep (x - zero)        a
    let healStep   = calStep (minOverFlow - x) b
    min attackStep healStep     

let R () = stdin.ReadLine () |> int

let N = R ()
let X = R ()
let A = R ()
let B = R ()

f N X A B |> printfn "%i"