Spell Crit Function - Help

Spell Crit Function - Help

Here is what i want to do to try to create a "Spell Crit" in Wc3.
W/e <unit> cast <spell>
Random Choose 1 from 1-5
1-Nothing
2-Nothing
3-Nothing
4-Deal X damage to triggering units spell target.
5-Nothing
Where the trigger would randomly choose a vairiable from 1 - 5 and do what the variable it randomed says to do. So 1-3 and 5 would do nothing and 4 would be the crit.

Help with actually doing this?

where exacly are you having problems?

If Random Integer Between 1 and 5 Equal to x then do actions.