Ok so now we're going to get to a quiz that's actually hard. It's not really hard, it just kind of feels hard, because I always screw it up. And that is, the Gaussian filter that we're talking about is referred to as a, as an exponential, and the complete formula here is what? So h of u, v is, by the way you see the exponents? They're the same everywhere. The only thing we're looking at that's constant. So, the question is, what's the right constant? One over 2 pi sigma squared, 1 over the square root of 2 pi sigma squared, 1 over the square root of 2 pi sigma.