Problemset link: https://codeforces.com/contestInvitation/dbdc3d98d7378b34a4a47114864882815a7669e9 Harmonic series blog: https://discuss.codechef.com/t/more-intuitive-explanation-for-the-harmonic-seriess-sum/67287 I end up covering problems A-H and K in the problemset. Here's part 2, where I finish it: https://www.youtube.com/watch?v=kCY8seazgFU Note that problem explanations are probably long because of interacting with chat, not necessarily because of difficulty. Also, sometimes I refer to the problemset as a "mashup" because Codeforces calls it that. Timestamps: Intro 00:00 Intro to DP (Fibonacci) 04:19 Mashup A 21:20 Mashup B 45:37 Trying to pin a message 52:05 Continuing B 56:25 Mashup C 1:08:49 Mashup D 1:30:45 Mashup E 1:46:22 Intermission (+ water bottle inspiration) 2:12:05 Mashup F 2:17:45 Figuring out what a derangement is 2:48:59 Mashup G 3:00:24 Mashup H 3:28:14 Mashup K 3:39:26