Summary table from pivot table

[alandilworth]

Hello,
I currently have the table below and I am trying to create a summary of this that only shows the aggregate of Sum(AllTimeMegaSales) for the Top Third, Middle Third, and Bottom Third.  For context this table shows the sum of sales for select territories.  The third column is a dynamic calculated field that groups the territories into thirds based on sales.

I want the end result to look like this table below.  Any help will be greatly appreciated!