Legaldose

Hello, I've just got a quick question about charging an object by conduction. I've been studying for my final and I came across a problem that I can't really see how to solve.

Say you have two conducting spheres, A and B. They are both exactly the same in every way except for their electric charge. Say A is electrically neutral and B has a charge of -3e. Now what happens when they touch? I was under the impression that when they come into contact they would share the charge equally, but you can't have a charge of -(3/2)e. So what happens?

Thanks, and happy physics!!