Two

Hermione looked up, shocked to see what appeared to be another her right in front of her. All the symptoms seemed to indicate she was under the effects of that duplication spell, but to see it with her own eyes was its own shocking matter. Good thing it ripped apart clothes as well, because it allowed Hermione to confirm that not a single spot was different between them. It wasn't an excuse for her to examine her own hot and sexy body, not at all.

"So if you're the exact same as me..." The two Hermiones spoke at the same time, seemingly confirming that the two were exactly the same. "Then who used the spell on us?"

"Who's there!?" The Hermiones froze. They were in the library and out in the dorms much later than they should, so if they were spotted here with a forbidden spell cast on them no less they could potentially be expelled. Luckily before coming here Hermione asked Harry for his Invisibility Cloak, and it was just snug enough to cover the two of them.

And so the two Hermiones hid under the cloak, hoping no one spotted them.