4 hands. ;3 I counted as much as 17 notes at a single time (most likely there's parts with more then that). :

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You can do it with only 3 hands... if you use a foot too
I'm doing it, I'm sorry I can't post a video
Ugh, and now that I think about it, I gave the latop to my mother and now, somehow, it doesn't work anymore... but she did not break it, no no

I still have the old one, but it barely works and the screen is always in funny colors... btw it was nice to see my teacher's face when I showed him, some years ago, a project now yellow, then red, then blue... :

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