Moral Dilemma - Hold the Door or no?

This happens to me on a daily basis.....

I'm walking into my office building, and I decide to be a nice guy and hold the door for the person after me.  While I'm busy patting myself on the back, I end up standing there holding the door for the next 15-20 people that come after me.

How do I gracefully keep being a nice guy, but only for the person immediately after me?  How do I hold the door for one person, instead of moonlighting as a doorman?

thoughts?