stdin.ReadLine() |> ignore
stdin.ReadLine().Split() 
|> Array.map(int)
|> Array.sort
|> Array.pairwise
|> Array.map(fun (a,b) -> b-a)
|> function 
    | x when x |> Array.forall (fun x -> x<>0) -> 
        x
        |> Array.distinct
        |> Array.length
        |> function | 1 -> "YES" | _ -> "NO"
    | _ -> "NO"       
|> printfn "%s"