Article : We get 2017 - Lycée Arago (Perpignan) Colegiul National B.P. Hasdeu (Buzau, Roumanie)

The question: "At the beginning you only have an empty blackboard. At each step you can either write twice the number 1 on the blackboard or delete two numbers equal to n already written and replace them by n-1 and n+1. How many steps at least will be necessary in order to reach the number 2017?"
A "good" strategy leads to the result much more efficiently than what can appear at first approach. Then, the authors give a complete description of the process, and determine the number of steps.