2). explain it to me I do not understand

Question

What is the output of this code ?
def func(x):
res = 0
for i in range(x):
res +=1
return res

Print (func(4))

Answer 1

But it's answer is 6

Answer 2

I don't understand

Answer 3

Let go and see
Python module 3 quiz
There answer 6 is provided