A movie theater charges $50$ Rupees for a ticket.
The cashier starts out with no change, and each change customer pays with a Rupees $50$ note or Rupees $100$ note (& gets change).
Clearly, the cashier will be in trouble if there are too many customers with $100$ rupees note.
It turns out that there are $2n$ customers, and cashier never had to turn them away, but after dealing with last customer, there were no $50$ rupees note left in cash register. Let $w_n$ denote the number of different ways this could have happened.