How to calculate the root of filtered members based on another filter

Hello All,

  Please find the below query.

with member agg as 
sum(

exists([Product].[OTC1].[OTC1],existing([Product].[Pack].[Pack])])
,[Measures].[Values HNA])

select 
agg on 0 from cube where [Product].[Product].&[101]

For a particular product am trying to know the existing packs associated with it and then finding the OTC1's for which we are having sales for a product. 

I want to find the total sales(all product sales) for the OTC1's which are having sales for the filtered product.

Note- In filtered it can be any other product attributes not only product so am going to the lowest level pack to identify the OTC1's.

Regards,

Bharath