Can someone explain Atcoder 269 Problem F solution?

Revision en1, by yh11, 2022-09-19 11:11:21

I just read Problem F editorial.

I realise that computing the sum of the box is not very difficult. (Its just some interpolation of the sum of first n natural numbers).

But in this editorial the answer has directly been provided and the explanation for the jumps in reasoning are skipped.

I was hoping someone could provide an explanation to fill in the gaps of this editorial.
Thanks. :)

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en2 English yh11 2022-09-19 11:14:01 107
en1 English yh11 2022-09-19 11:11:21 504 Initial revision (published)