can someone help me how to write this function block please

def learn(n):

""" Compute the combinations of size 2 from a set of size n

(n learn 2).

Function parameter:

n - an integer, the number of people in the room

The function returns an integer value, the number of combinations

of size 2 from a set of size n, given by the formula

n(n-1)/2 for n >= 2

0 for n < 2