how do you do this: if [long condition] then blah else blah?

how do you do this:

if:
The sum of the mana of all the units in UNIT-GROUP < 80
then:
do nothing
else:
skip remaining actions

?

Action:
Set Variable (mana) = 0
Pick all units in (unit group) and do set variable (mana )=(mana)+(Unit property -->mana)
if(mana<80,00) then do nothing else skip rem. actions.


where mana has to be a real variable.