open System
type Sol() =
    member this.Solve() = 
        let N = stdin.ReadLine() |> int
        let A = stdin.ReadLine().Split(' ') |> Array.map int |> Array.sort 
        let pairA = Seq.pairwise A |> Seq.map (fun (x,y) -> (y - x)) |> Seq.distinct
        let yesno = ((Seq.distinct A |> Seq.length) = N) && (Seq.length pairA) = 1
        if yesno = true then Console.WriteLine("YES") else Console.WriteLine("NO") 

let mySol = new Sol()
mySol.Solve()