How about: 13 months, each is always 28 days/4 weeks. At the end of the year there is a public holiday. Every leap year the public holiday is 2 days long. The h

How about: 13 months, each is always 28 days/4 weeks. At the end of the year there is a public holiday. Every leap year the public holiday is 2 days long. The hard part will be thinking of the name for the 13th month.