Go to any large music festival, and you’re bound to find an armada of public toilets. But, by the time it’s your turn to use one these fine establishments of human ingenuity, the situation inside may be less-than-ideal. Here’s how math can help ensure you get the cleanest spot when it’s your time to go.

In the Numberphile video below, Dr. Ria Symonds, of the University of Nottingham, gives you a logical way to ensure you find the cleanest toilet. “There’s always lots of toilets to choose from,” she explains. “The problem with these toilets is they’re not always that well looked after.” Check out the video, and let us know your thoughts.