An interstellar hotel
Source: All-Russian Olympiad 2019 grade 10 problem 3
April 23, 2019
combinatoricsconstruction
Problem Statement
An interstellar hotel has rooms with capacities people. These rooms are occupied by people in total. Now a VIP guest is about to arrive and the owner wants to provide him with a personal room. On that purpose, the owner wants to choose two rooms and and move all guests from to without exceeding its capacity. Determine the largest for which the owner can be sure that he can achieve his goal no matter what the initial distribution of the guests is.