MathFest Day Four Challenge Problem

No more MathFest after today, but we're not stopping early! Here's the last Challenge Problem, which puts a spin on a mathematical construct you may well know and love already.

 Like before, if you're at MathFest and you show us you've solved the problem before we put the answer up this afternoon, you could win some cool Center of Math stuff! Make sure to check out our booth (19) if you haven't already. If you've enjoyed these, our Problems of the Week will continue onward on Monday, so don't worry that these problems are going away.