Palindromic Subsequence 

A Subsequence is a sequence obtained by deleting zero or more characters in a string. A Palindrome is a string which when read from left to right, reads same as when read from right to left. Given a string, find the longest palindromic subsequence. If there are many answers to it, print the one that comes lexicographically earliest.

Constraints

• Maximum length of string is 1000.
• Each string has characters `a' to `z' only.

Input 

Input consists of several strings, each in a separate line. Input is terminated by EOF.

Output 

For each line in the input, print the output in a single line.

Sample Input 

aabbaabb
computer
abzla
samhita

Sample Output 

aabbaa
c
aba
aha