fun readStr () =
    let
        fun scan reader stream = SOME (StringCvt.splitl (not o Char.isSpace) reader (StringCvt.skipWS reader stream))
    in
        valOf (TextIO.scanStream scan TextIO.stdIn)
    end


val () =
    let
        val s = readStr ()

        val ans = if String.sub (s, 0) = String.sub (s, 1) andalso String.sub (s, 0) <> String.sub (s, 2)
                  then "Yes"
                  else "No"
    in
        print (ans ^ "\n")
    end