Prompt while executing a macro

Hi Gurus,

I need help in writing a logic for a macro for the below scenario:

Scenario: Copy values from KF1 to KF2 based on user input in the planning book.

If the user wants to adopt 75% or 125% or 150% or whatever may be the percentage of KF1 to be copied to KF2, we want the user to able to input those values interactively and then the macro should compute and update KF2.

Can anyone provide step by step approach to achieve this?

Thanks,

Murali