うるう年

A leap year (in the Gregorian calendar) occurs:

• In every year that is evenly divisible by 4.
• Unless the year is evenly divisible by 100, in which case it's only a leap year if the year is also evenly divisible by 400.

Some examples:

• 1997 was not a leap year as it's not divisible by 4.
• 1900 was not a leap year as it's not divisible by 400.
• 2000 was a leap year!

Your task is to determine whether a given year is a leap year.