Filter By ASpath in mikroitk

How i want to write Rule That Filter By ASpath in mikoritk

Conditions
As-patch lenght 3 or 4

Aspatch=10:20:xxx:xxx

XXX any As number

Thanks
AS 10 router level1 (Uplink AS20)
AS 20 Router level 2 (Provide Internet and announce To IXP peers)

https://wiki.mikrotik.com/wiki/Manual:Routing/Routing_filters

i think use regex for filter by as path