need a smarter formula depending on user input

Hi,

Just wandering whether there is a better formula when it comes to Sum based on user input, for example, if user input 15 on cell S5, formula should be automatically Sum the last 15 months, Currently i have a crappy formula that works, but i am just lazy to write all the code as the number will go up to 24 months.

Please Login or Register  to view this content.

Thanks
Lex

s9:

Please Login or Register  to view this content.