Write a program that accepts a year and determines whether or not the year is a leap year. Use the mod function. The output should be the variable extra_day, which should be 1 if the year is a leap year and 0 otherwise. The rules for determining leap years in the Gregorian calendar are:

1. All years evenly divisible by 400 are leap years.

2. Years evenly divisible by 100 but not by 400 are not leap years.

3. Years divisible by 4 but not by 100 are leap years.

4. All other years are not leap years.
For example, the years 1800, 1900, 2100, 2300, and 2500 are not leap years, but 2400 is a leap year.