Question: 
Write a function to calculate the sum of the positive integers of n+(n-2)+(n-4)... (until n-x =< 0).


Model's Code:
def sum_series(n):
    return sum(i for i in range(n, 0, -2))



Sample Correct Code:
def sum_series(n):
  if n < 1:
    return 0
  else:
    return n + sum_series(n - 2)


Asserts:
assert sum_series(6)==12
assert sum_series(10)==30
assert sum_series(9)==25


Tests:
Test 1 of 3: PASS
Test 2 of 3: PASS
Test 3 of 3: PASS

Test 162 of 974: 118/162 (72.8395061728395%): success