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


fun quicksort [] = []
  | quicksort (h::tl) =
    let 
        val (s, b) =
            List.foldl
                (fn (x, (small, big)) =>
                    if x <= h then (x::small, big)
                    else (small, x::big))
                ([], [])
                tl
    in
        (quicksort s) @ [h] @ (quicksort b)
    end


fun isSatisfy l =
    let
        fun isSatisfyAux _ nil = true
          | isSatisfyAux _ [_] = true
          | isSatisfyAux diff (h1::h2::tl) =
            if h2 - h1 = diff then isSatisfyAux diff (h2::tl)
            else false

        val (h1::h2::tl) = quicksort l
    in
        if h2 - h1 = 0 then false
        else isSatisfyAux (h2 - h1) (h2::tl)
    end


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

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