How many lines, as a function of n (in (.) form), does the following program print?

How many lines, as a function of n (in Θ (.) form), does the following program print?

Write a recurrence and solve it.(Average case)

function f(n):

res=0

if n ≤ 1:

res 1

else:

for i in range (n):

res += f(i) * f(n – i – 1)

print (res)

return res