MathDB
Rich knight adds coins

Source: 239 MO 2024 S2

May 22, 2024
combinatorics

Problem Statement

A rich knight has a chest and a lot of coins, so every day he puts into the chest some quantity of coins - among the numbers 1,2,,1001, 2, \ldots, 100. If there exist two days on which he added equal quantities of coins (say, kk coins) and he has added in total at most 100k100k coins on the days between these two days, he stops putting coins into the chest. Prove that this will necessarily happen eventually.