Minimum Length of String After Operations

Description

You are given a string s.

You can perform the following process on s any number of times:

- Choose an index i in the string such that there is at least one character to the left of index i that is equal to s[i], and at least one character to the right that is also equal to s[i].

- Delete the closest occurrence of s[i] located to the left of i.

- Delete the closest occurrence of s[i] located to the right of i.

Return the minimum length of the final string s that you can achieve.