Can anyone provide a proper explanation of the A2 problem of Round 2 Facebook Hackercup editorial provided here: https://www.facebook.com/codingcompetitions/hacker-cup/2022/round-2/problems/A2/solution

I could not understand the Video editorial as well.

If you have other solution, kindly explain it. I want to learn and upsolve it. It is indeed a good question. Providing code/implementation the explanation is highly appreciated. Thanks!