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


fun readLargeInt () =
    valOf (TextIO.scanStream (LargeInt.scan StringCvt.DEC) TextIO.stdIn)


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

        val ans =
            if
                (List.foldl
                     (fn (x, acc) =>
                         x + acc)
                     0
                     x_s) = a * (Int.toLarge n)
            then "YES"
            else "NO"
    in
        print (ans ^ "\n")
    end