The big moon is 3 1 day and the small moon is 3 days. The difference between a normal year and a leap year is only in February.

The number of years in A.D. can be divisible by 4 into leap years, but the number of whole hundred years (both single digits and ten digits are acceptable) must be divisible by 4 into leap years (for example, 19 is not a leap year), and everything else is a flat year.