Python - What does happen in this code? Why is output 18?

Question

arr = [0,1,2,3,4,5]
sum = 0
for n in arr:
sum = sum + n
if(n==3):
arr.insert(n,10)
print (arr)
if(sum>15):
break
print (sum)

Answer 1

n is added to the sum first.
When n == 3, 10 is inserted to index 3. Then the iteration continues. The next element is still 3 because 10 is inserted. 3 is added again and 10 is inserted again because n == 3. And again, again, again....Until sum > 15 it breaks
0+1+2+3+3+3+3+3 = 18 (Done 5 times)