Replace the question mark with a number

One day a college professor of Psychology was greeting his new college class. He stood up in front of the class and said, "Would everyone who thinks he or she is stupid please stand up?"

After a minute or so of silence, a young man stood up.

"Well, good morning. So, you actually think you're a moron?" the professor asked.

The kid replied, "No sir, I just didn't want to see you standing there all by yourself."