MathDB
Drawing segments

Source: All-Russian 2022 11.4=10.4

April 19, 2022
combinatoricsgraph

Problem Statement

Given is a natural number n>4n>4. There are nn points marked on the plane, no three of which lie on the same line. Vasily draws one by one all the segments connecting pairs of marked points. At each step, drawing the next segment SS, Vasily marks it with the smallest natural number, which hasn't appeared on a drawn segment that has a common end with SS. Find the maximal value of kk, for which Vasily can act in such a way that he can mark some segment with the number kk?