https://codeforces.me/contest/1783/problem/C

This is the link of the problem

https://codeforces.me/blog/entry/111194

This is the tutorial

In the editorial for problem C , why is it written we should check

m+b[ans-1]>=a[ans]

why is it depending on a , as it is not in any ordered pair , rather isn't it much logical that we will check with b[ans] that is it possible that instead of this we can switch it up with next element possible.

If anyone can help in pointing out where I am going wrong.