Given a string s, return the longest substring of s that is a palindrome.

A palindrome is a string that reads the same forward and backward.

If there are multiple palindromic substrings that have the same length, return any one of them.

Example 1:

Input: s = "ababd"

Output: "bab"

Explanation: Both "aba" and "bab" are valid answers.

Example 2:

Input: s = "abbc"

Output: "bb"

Constraints:

• 1 <= s.length <= 1000
• s contains only digits and English letters.