fun readInt () =
    valOf (TextIO.scanStream (Int.scan StringCvt.DEC) TextIO.stdIn)


fun isSatisfy n l min diff =
    let
        val checkList = Array.array (n, false)

        fun check nil = true
          | check (h::tl) =
            let
                val index = (h - min) div diff
            in
                if Array.sub (checkList, index) = false
                then
                    (
                      (
                        Array.update (checkList, index, true);
                        check tl
                      )
                    )
                else false
            end
    in
        if diff = 0 then false
        else check l
    end


val () =
    let
        val n = readInt ()
        val x_s = List.tabulate (n, fn _ => readInt ())

        val (min, max) = List.foldl
                             (fn (x, (minAcc, maxAcc)) =>
                                 (Int.min (x, minAcc), Int.max (x, maxAcc)))
                             (100000000, 0)
                             x_s

        val d = (max - min) div (n - 1)

        val ans = if isSatisfy n x_s min d then "YES"
                  else "NO"
    in
        print (ans ^ "\n")
    end