code: public static long adjustWatermark(String baseWatermark, int diff) {
      SimpleDateFormat parser = new SimpleDateFormat(INPUTFORMAT);
      Date date = Utils.toDate(baseWatermark, INPUTFORMAT, OUTPUTFORMAT);
      return Long.parseLong(parser.format(Utils.addDaysToDate(date, diff)));
    }
docs: Adjust the given watermark by diff
  
  @param baseWatermark the original watermark
  @param diff the amount to change
  @return the adjusted watermark value