Greetings Codeforces,

I would like to invite you all to CODEJUNK 2020, the competitive coding competition of Techniche, IIT Guwahati's annual Technical Fest, and which is being held in collaboration with The Coding Club of IIT Guwahati.

The contest will be held on CodeChef and will start at 20th July 2020, 20:00 hrs IST. You will have 5 problems to solve in 2hours. The ranklist will be ICPC style with the penalty set to 10 minutes.

The problems have been prepared and tested by me (zeus_iitg), Nishchay Manwani (EnEm) and Tejas Khairnar (BrownieTK).

You can also register for prizes and laddus worth Rs. 50,000 along with assured coupons worth Rs. 200 with a registration fee of Rs. 100.

For more information visit techniche.org/techolympics

Good luck. :)

NOTE: Registration is only for prizes. You can participate without registering as well.

Critical Cities

Link to problem: Critical Cities

Kindly share your approach to solve this problem.

Any help is highly appreciated.

Link to the problem: Bulbs | CodeChef

Kindly share your approach for solving this problem.

Problem Description

You are given an integer N.

Find the sum of floor( i / j ) for all pairs i, j (1 <= i, j <= N) such that i and j are coprime.

N <= 100000

Link to problem