public int principleTerm(int y, int m) {
		if (y < 1901 || y > 2100)
			return 0;
		int index = 0;
		int ry = y - baseYear + 1;
		while (ry >= principleTermYear[m - 1][index])
			index++;
		int term = principleTermMap[m - 1][4 * index + ry % 4];
		if ((ry == 171) && (m == 3))
			term = 21;
		if ((ry == 181) && (m == 5))
			term = 21;
		return term;
	}