import java.lang.*;
import java.util.*;

class LongestPalindrome {
	public static String longestPalindrome(String s) {
		// TODO: check if s length is 0 or 1
		// TODO: find simpler solution

		s = s.toLowerCase();
		char[] arr = s.toCharArray();
		String ans = null;

		int i = 0;
		int j = 0;
		int max = 0;
		// Odd case: "aba"
		for (int a = 1; a < arr.length - 1; a++) {
			i = a - 1;
			j = a + 1;
			while (i >= 0 && j < arr.length) {
				if (arr[i] == arr[j]) {
					if (j - i > max) {
						max = j - i;
						ans = s.substring(i, j + 1);
					}
					i--;
					j++;
				} else {
					break;
				}
			}
		}
		// Even case: "abba"
		for (i = 0, j = i + 1; i < arr.length - 1; i++) {
			while (i >= 0 && j < arr.length) {
				if (arr[i] == arr[j]) {
					if (j - i > max) {
						max = j - i;
						ans = s.substring(i, j + 1);
					}
					i--;
					j++;
				} else {
					break;
				}
			}
		}
		return ans;
	}

	public static void main(String[] args) {
		String s = "kl;fadsjf;dalscbbciuporeqwrpo";
		System.out.println(longestPalindrome(s));
	}
}