Crystal Reports Last date of each month and for one sales

Message

   Hi All,

I get from a stocked procedure (SP) a date field, a sales name and assets.

Rows             Date              Sales          Assets
Row1             Nov 1st   -->    S1              10
Row2             Nov 8th   -->    S1              12
Row3             Nov 15th -->    S1              13  
Row4             Nov 1st   -->    S2              20
Row5             Nov 8th   -->    S2              22

Row6             Dec 2nd   -->    S1              12
Row7             Dec 9th    -->    S1              11  

I would like to get only last updated assets for one month and one sales ie red lines 3, 5 and 7 above.
How can I get them through a formula in a CR11 or by adding a condition into the SP.

Many thanks
Mohamed