How to sum values for to get a accumulative total value

Question

Hi,

Just i want to create a new column from sum accumulative values begins from last record:

 

for example in this image it is used a OVER (PARTITION BY clause in the field CATEGORY to calculates retencion_value_3_week , but  i want to keep the values from the first record to get a TOTAL accumulative value at the end or records:

 

 I mean not to get "6" in the first record of category B in retencion_value_3_week, but "26"  and after sum "15" to get not "21" but "41"

 

Thanks...