How to check if less than 2 of 3 variables are empty

I need to check that there are at least 2 values before running a script, but can't seem to get the condition to fire.

When I use if (risForm) {... the script runs when risForm is filled, and when I use if (!(risForm)) {... the script runs if risForm is empty, but I can't seem to work out how to check if any 2 of the three is full... I've tried this:

if ((!(risForm)) + (!(runForm)) + (!(angForm)) < 2) {...

along with a numerous adjustments to precise formatting/bracketting, but it's not getting me anywhere!