12 month sum indicator

Hi,

let assume we have data like this :

I would like to create measure that will be working as 12 months sum but only in 12 months period of time : time <= maxdate, time >= maxdate - 12.

I have created a measue like this :

I would like to get a view like this ( alwyays for last 12 months )  and count how many of values per month was negative.