Cool level. My first attempt was 10-off, but was surprisingly close to the correct solution - I just needed to execute the same ideas more intelligently. Fun solution though.
Interesting. I tried some "fancy" (read: stupid) stuff at first that didn't really get me close, and then when I tried what felt more intuitive and obvious, it worked. Admittedly my second path involved a few ideas from my first, but I'm surprised that the solution felt as simple as it did.