How would I set this up in R?

You and a friend are meeting up a local pizza parlor for dinner. To order a pizza you have your choice of N = 19 different toppings. Though you are great friends, you never agree on pizza toppings so you are both going to order your own pizza. If you and your friend order independently, and both of you randomly select which toppings you get on your pizza, what is the probability that you order the same toppings on your respective pizzas?