I take one step at a time and count stairs on my left foot (but don't alter my walking pattern). So if I happen to start taking the stairs on my left foot, I'll count 1-3-5-7, etc., otherwise it's 2-4-6-8. It can switch between evens or odds whenever landings are involved.

I know the # of stairs per flight at home and at work, not sure about other places though.