Every three years, more than 30 million Hindu worshippers gather for the Kumbh Mela in India, the world's largest religious gathering, in order to wash away their sins. With massive crowds descending on small cities and towns, stampedes inevitably happen, and in 2003, 39 people were killed during the festival. In 2014, then 15-year-old Nilay Kulkarni decided to put his skills as a self-taught programmer to use by building a tech solution to help prevent stampedes. Learn more about his invention -- and how it helped the 2015 Nashik Kumbh Mela have zero stampedes and casualties.