[lmartel]

This may not have been a serious question but I'll give a serious answer: depending on the interviewer, you could get bonus points for going "above and beyond" or, yes, you could be penalized for "not reading the spec."

I've found that the best way to handle it in a conventional whiteboard interview is to mention it when appropriate and offer to add the functionality later.

"Now, here's the part of the code where I'd deal with odd N. Since we're guaranteed even N in the problem statement I'll skip this for now, but we can come back to harden this function later if you like."