int	Calendar::DayOfWeek(int day, int month, int year, int zelleroffset)
{
	if(month < 3)
	{
		month += 12 ;
		year -= 1 ;
        }

	int n1 = (26 * (month + 1)) / 10;
	int n2 = (125 * year) / 100;

	return ((day + (8 - first_day) + n1 + n2 - (year / 100) + (year / 400) - zelleroffset) % 7 );
}