A leap year is a calender year that contains 366 days (the extra
day is the 29th of February), and it comes after every four
years.
To check if a year is a leap year, divide the year by 4.
If a year is fully divisible by 4, it is a leap year. For
example, the year 2016 is divisible 4, so it is a leap year,
whereas, 2015 is not.
However, Century years like 300, 700, 1900, 2000 need to be
divided by 400 to check whether they are leap years or not.