let f () =
    let m = (stdin.ReadLine ()).Split ' ' |> Array.map int
    let n = stdin.ReadLine () |> int
    let a = (stdin.ReadLine ()).Split ' ' |> Array.map int
    seq { for i in 0..n-2 -> a.[i]*m.[1]>a.[i+1]*m.[0] }
    |> Seq.tryFind (fun b -> b=true)
    |> function
        | Some (true) -> "NO"
        | None -> "YES"
f () |> printfn "%s"