What value is returned by the following function? Express your answer as a function of n. Give the worst-case running time using Big Oh notation.

function prestiferous (n)

r:=0

for i := 1 to n do

for j := 1 to i do

for k := j to i + j do

for l := 1 to i + j - k do

r := r + 1

return(r)