One, like most people.

But the more interesting question is: how long can you go with too little sleep? Like, with 3-4h naps? Or a few 30 min naps?

Obviously much longer, as anyone with little children or a tight thesis deadline can tell you. But I catch myself making mistakes and generally saying and doing things I shouldn't, quite similarly to mild alcohol intoxication. I would describe 2-3 days with too little sleep as maybe 3-4 beers, you can still force yourself to focus, but you really shouldn't drive or write that important letter any more.