[36 / 4 / ?]
Let's see it this works
Each flag starts with 10
For each post of the same flag:
>ID starting with a letter: +last_digit
>ID starting with a number: -last_digit
Goal: Reach zero
Each flag starts with 10
For each post of the same flag:
>ID starting with a letter: +last_digit
>ID starting with a number: -last_digit
Goal: Reach zero