# coding=utf-8
"""
Return the sum of the numbers in the array, returning 0 for an empty array.
Except the number 13 is very unlucky, so it does not count and numbers that come
 immediately after a 13 also do not count.

sum13([1, 2, 2, 1]) → 6
sum13([1, 1]) → 2
sum13([1, 2, 2, 1, 13]) → 6
"""
def sum13(nums):
  sum=0
  i=0
  while i<=len(nums)-1:
    if nums[i]!=13:
      sum+=nums[i]
      i+=1
    else:
      i+=2
  return sum