Given a string `s`. In one step you can insert any character at any index of the string.

Return the minimum number of steps to make `s` palindrome.

A Palindrome String is one that reads the same backward as well as forward.

Example 1:

    Input: s = "zzazz"
    Output: 0
    Explanation: The string "zzazz" is already palindrome we don't need any insertions.

Example 2:

    Input: s = "mbadm"
    Output: 2
    Explanation: String can be "mbdadbm" or "mdbabdm".

Example 3:

    Input: s = "leetcode"
    Output: 5
    Explanation: Inserting 5 characters the string becomes "leetcodocteel".

Constraints:

- `1 <= s.length <= 500`
- `s` consists of lowercase English letters.