You notice a progress bar that jumps to 50% completion. Apparently, the door isn't yet satisfied, but it did emit a star as encouragement. The instructions change:

Now, instead of considering the next digit, it wants you to consider the digit halfway around the circular list. That is, if your list contains 10 items, only include a digit in your sum if the digit 10/2 = 5 steps forward matches it. Fortunately, your list has an even number of elements.

For example:

1212 produces 6: the list contains 4 items, and all four digits match the digit 2 items ahead. 1221 produces 0, because every comparison is between a 1 and a 2. 123425 produces 4, because both 2s match each other, but no other digit has a match. 123123 produces 12. 12131415 produces 4. What is the solution to your new captcha?