/* Zeller's Congruence to determine day of week */
int get_dayofweek(int date)
{

 int d = date % 100;
 int m = (date % 10000) / 100;
 int y = date / 10000;

 if (m < 3)
 {
	 m = m + 12 ;
	 y = y - 1;
 }

 return ((2 + d + (13*m-2)/5 + y + y/4 - y/100 + y/400) % 7);

}

int main(void)
{

	/* my birthday */
	int bday = get_dayofweek(19800110);
	char *d;

	switch(bday)
	{
	case 0:
		d = "Sunday";
		break;
	case 1:
		d = "Monday";
		break;
	case 2:
		d = "Tuesday";
		break;
	case 3:
		d = "Wednesday";
		break;
	case 4:
		d = "Thursday";
		break;
	case 5:
		d = "Friday";
		break;
	case 6:
		d = "Saturday";
		break;
	}

	printf("%s\n", d);
}