# Know some history before doing math

Level pending**Zeller's congruence** is an algorithm devised by Julius Christian Johannes Zeller to calculate the day of the week for any Julian or Gregorian calendar date. For the Gregorian Calendar, the formula is

\[w=\bigg ( y +\bigg \lfloor \frac{y}{4} \bigg\rfloor + \bigg\lfloor \frac{c}{4} \bigg\rfloor -2c + \bigg\lfloor \frac{26(m+1)}{10}\bigg\rfloor+ d-1\bigg) \mod 7\]

What is the earliest date when the formula could be applied to calculate the day of the week?

Hint : Gregorian Calendar

**Your answer seems reasonable.**Find out if you're right!

**That seems reasonable.**Find out if you're right!

Already have an account? Log in here.