Need customer Exit for user enter calyear dynamically displaying fiscal periods

Hi Experts,

How to write Customer Exit.

Example -- User enter year- 2013

Then I want to display fiscal period 001.2013 to 004.2014.

If user enter - 2012

Then I want to display fiscal period 001.2012 to 004.2013.

I want to write customer exit, where user enters year dynamically, then I want to display fiscal periods

Thanks

Sunil