code: public String getShroveTideWeekOrthodox(int year){
          String easterOrthodox = getEasterSundayOrthodox(year);
          SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
          try{
              Calendar calendar = Calendar.getInstance();
              Date date = formatter.parse(easterOrthodox);
              calendar.setTime(date);
              calendar.add(Calendar.DAY_OF_MONTH, -49);
              int shroveTideWeek =  calendar.get(Calendar.WEEK_OF_YEAR);
              if(shroveTideWeek<10){
                  return year+"-W0"+shroveTideWeek;
              }
              return year+"-W"+shroveTideWeek;
          }
          catch (ParseException pe){
              Logger.printError("ParseException:"+pe.getMessage());
              return "unknown";
          }
      }
docs: Get the date of the Shrove-Tide week in a given year
  
  @author Elena Klyachko
  @param year
  @return date