After listening for about 2 hours.. I was watching Howl's Firebase lecture, and since Firebase didn't work because of the version, I took this lecture to learn Kotlin as well. After listening for about 2 hours, I think it was a good decision to pay. It's still unfamiliar, but if you're a major like me, I think it won't be difficult to learn. However, beginners might find it a little unfamiliar, confusing, or difficult, but as Howl said, I think it'll be more fun to learn by first using this language and learning the theory. Now that I've seen the class side, I want to quickly study Android and Firebase and make a portfolio. Thank you for the great lecture!