I am looking to count the number of users whose property is greater than a threshold

Is this example, I have a property called “media count” for the event “export” which counts the number of media exported each time by each user. I would like to know how many users exported more than 250 media in a month.

I was able to select the segment of users “sum of media count per users” >= 250 with PROPSUM(a) but how can I count these unique users? For now the workaround is to group by userid but it it not clean at all 

Thanks !