Подскажите в чем причина?
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
      String month =  reader.readLine();
      SimpleDateFormat dateFormat = new SimpleDateFormat("MMMMM", Locale.ENGLISH );
      Calendar calendar = new GregorianCalendar();
      calendar.setTime(dateFormat.parse(month));

      int m = calendar.get(Calendar.MONTH) + 1;
      System.out.println(month + " is the " + m + " month");