MathDB
Stop Azer :)

Source: Turkey Olympic Revenge 2024 P6

August 6, 2024
combinatoricsalgebra

Problem Statement

Let nn be a positive integer. On a number line, Azer is at point 00 in his car which have fuel capacity of 2n2^n units and is initially full. At each positive integer mm, there is a gas station. Azer only moves to the right with constant speed and doesn't stop anywhere except the gas stations. Each time his car moves to the right by some amount, its fuel decreases by the same amount. Azer may choose to stop at a gas station or pass it.
There are thieves at some gas stations. (A station may have multiple thieves) If Azer stops at a station which have k0k\ge 0 thieves while its car have fuel capacity dd, his cars new fuel capacity becomes d2k\frac{d}{2^k}. After that, Azer fulls his cars tank and leaves the station. Find the minimum number of thieves needed to guarantee that Azer will eventually run out of fuel.
Proposed by Mehmet Can Baştemir and Deniz Can Karaçelebi