private int getNumOfSundaysOnMonthFirst(int yearStart, int yearEnd) {
		int sumSunday = 0;
		int dayStart = getDayStart(yearStart);
		for (int i = yearStart; i <= yearEnd; i++) {
			for (int j = Calendar.JANUARY; j <= Calendar.DECEMBER; j++) {
				if (dayStart == Calendar.SUNDAY) {
					sumSunday++;
				}
				int days;
				if (j == Calendar.FEBRUARY) {
					if (isLeapYear(i)) {
						days = 29;
					} else {
						days = 28;
					}
				} else if (j == Calendar.APRIL || j == Calendar.JUNE || j == Calendar.SEPTEMBER || j == Calendar.NOVEMBER) {
					days = 30;
				} else {
					days = 31;
				}
				dayStart = getDayStart(dayStart, days);
			}
		}
		return sumSunday;
	}