Thử thách đếm ngược ác liệt cho người dùng cao cấp!

This is not an exercise - but a technique for experts and advanced users. A top-class provocation that will put your skills and strength to the test! This is NOT to be trifled with! We're going to exploit your full potential today. Let's see how much you can control yourself. I hope you can withstand the pressure, because it's going to be pretty nasty ;)