You are given a string `s` consisting only of letters `'a'` and `'b'`. In a single step you can remove one palindromic subsequence from `s`.

Return the minimum number of steps to make the given string empty.

A string is a subsequence of a given string if it is generated by deleting some characters of a given string without changing its order. Note that a subsequence does not necessarily need to be contiguous.

A string is called palindrome if is one that reads the same backward as well as forward.

Example 1:

    Input: s = "ababa"
    Output: 1
    Explanation: s is already a palindrome, so its entirety can be removed in a single step.

Example 2:

    Input: s = "abb"
    Output: 2
    Explanation: "abb" -> "bb" -> "".
    Remove palindromic subsequence "a" then "bb".

Example 3:

    Input: s = "baabb"
    Output: 2
    Explanation: "baabb" -> "b" -> "".
    Remove palindromic subsequence "baab" then "b".

Constraints:

- `1 <= s.length <= 1000`
- `s[i]` is either `'a'` or `'b'`.