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+--- Day 21: Chronal Conversion ---
+
+You should have been watching where you were going, because as you wander the new North Pole base,
+you trip and fall into a very deep hole!
+
+Just kidding.  You're falling through time again.
+
+If you keep up your current pace, you should have resolved all of the temporal anomalies by the next
+time the device activates. Since you have very little interest in browsing history in 500-year
+increments for the rest of your life, you need to find a way to get back to your present time.
+
+After a little research, you discover two important facts about the behavior of the device:
+
+First, you discover that the device is hard-wired to always send you back in time in 500-year
+increments. Changing this is probably not feasible.
+
+Second, you discover the activation system (your puzzle input) for the time travel module. 
+Currently, it appears to run forever without halting.
+
+If you can cause the activation system to halt at a specific moment, maybe you can make the device
+send you so far back in time that you cause an integer underflow in time itself and wrap around back
+to your current time!
+
+The device executes the program as specified in manual section one and manual section two.
+
+Your goal is to figure out how the program works and cause it to halt.  You can only control
+register 0; every other register begins at 0 as usual.
+
+Because time travel is a dangerous activity, the activation system begins with a few instructions
+which verify that bitwise AND (via bani) does a numeric operation and not an operation as if the
+inputs were interpreted as strings. If the test fails, it enters an infinite loop re-running the
+test instead of allowing the program to execute normally.  If the test passes, the program
+continues, and assumes that all other bitwise operations (banr, bori, and borr) also interpret their
+inputs as numbers. (Clearly, the Elves who wrote this system were worried that someone might
+introduce a bug while trying to emulate this system with a scripting language.)
+
+What is the lowest non-negative integer value for register 0 that causes the program to halt after
+executing the fewest instructions? (Executing the same instruction multiple times counts as multiple
+instructions executed.)
+
+