VTMO 2026 - Grade 5 - Semifinal - SET 11 - Self-study Question 22

A machine processes a natural number repeatedly until it reaches 0. If the current number is even, it divides it by 2; if it is odd, it subtracts 1. Find the smallest starting number that takes exactly 7 steps to reach 0.
For example, $6\to3\to2\to1\to0$ takes 4 steps.