Problem of the Week #6

Thanks for sending your solutions to Problem of the Week #5! We even had submissions from professors here (although they’re not qualified of course)! Anyway we received two correct solutions from undergraduates, and the first was Zachary Hancock, and the second was Brendan Caseria. Congrats to Zachary and Brendan!

Now #6 is the following:
0019_POW_2015_11_11