Bonus day !
Despite your best efforts to get Santa’s submarine out of trouble, data scientists couldn’t prevent it from crashing onto the seafloor and crushing all the crabs into some kind of surimi paste. Unfortunately, the submarine had an AI embedded into its onboard computers to help with the navigation. The AI was already dying (hence all the problems you had to solve this year), but the crash definitely brought its life to an end.
However, the AI was so loyal to the mission that its spirit remains somewhere between this world and the digital afterworld to send you some words of wisdom for the upcoming year (your puzzle input).
Your mission consists in receiving and decrypting the messages sent by the AI spirit.