A palindrome is a sequence of characters
that reads the same backwards and forwards.

Given a string, s, find the longest palindromic
substring in s.

Example:

Input: "banana"
Output: "anana"

Input: "million"
Output: "illi"

```python
class Solution
  def longestPalindrome(self, s):
    # Fill this in.

# Test program
Solution().longestPalindrome("tracecars")
# racecar
```