Crystal Reports How to implement Top N rank as a prompt?

Message

     I want to display a static prompt in my crystal report such that Users should be able to select the Top N filter in the report.

Example: Select the Top N or Bottom N from the FOllowing prompt:

Where N =  Top 10
                   Top  15
                   Bottom 10
                   Bottom 15
                   Top 30

How do I implement this in my report?

TIA