Kill a number of unit in region >.<

lol i have a verry stupid problem,

i want it so that when a unit enters a region and there are more then 7 of a unit type anywhere on the map it kill as many it needs that 7 of this units stay alife,

example

if there are 11 units of that type anywhere on the map it kills 4
if there are 20 units of that type anywhere on the map it kills 13.. ect.

i tried some trigger, once it killed all units, any other time game crashed :\

here, try this

thank you, i can handle whit that :>