Help with using the MAX function in a custom column

Hi,

I need to create a custom column using a DAX statement.  I'm pretty sure I need to use the MAX or MAXX function to accomplish what I'm trying to do here.

Specifically, I need the new column to return the [Members] for each [GroupID]...but only in the row where that GroupIDs [MonthEnd] date is the latest.

Here is an example of the current table:

I want to add a new column to this table called MaxMonthEnd that would return the following results for each row:

Please let me know if you need any other detail for this.  I'll be monitoring the thread closely.  

Thank you!

Andrew