You are given a string seq made up only of the characters 'A' and 'B'.

You may repeatedly perform the following operation:

• Delete any occurrence of the substring 'AB' or 'BB'.
• After deletion, the remaining parts of the string are concatenated.

Your task is to determine the minimum possible length of the string after performing any number of valid deletions.

Note: A substring refers to a contiguous sequence of characters.

Return the minimum remaining length.