sing Big Oh notation, what is the tightest upper bound for the running time of the below function fun?

def fun$($n$)$: # n is a positive integer

count $=0$

i $=$ n

while i $>0$:

for j in range$($n$)$:

count $+=1$

i $//=4$ # Integer division rounds down

return count

Group of answer choices

O$($n log n$)$

Unbounded

O$($log n$)$

O$($n$^2)$

O$($n$)$