#include <cstring>

#include <iostream>

using namespace std;

class Solution {

public:

string longestPalindrome(string s) {

// Start typing your C/C++ solution below

// DO NOT write int main() function

if(s == "")

return "";

int max = -1;

string result;

int length = s.length();

int g1,g2;

for(int i = 0;i < length;i++)

{

g1 = get11(s,i);

g2 = get12(s,i);

if(g2 > g1)

{

if(g2*2 > max)

{

result = s.substr(i-g2+1,g2*2);

max = g2*2;

}

}

else

{

if(g1*2+1>max)

{

result = s.substr(i-g1,g1*2+1);

max = g1*2+1;

}

}

}

return result;

}

int get11(string s,int p)

{

int i = 1;

int count = s.length();

while((p-i)>=0&&(p+i)<count&&s[p-i]==s[p+i])

{

i++;

}

return --i;

}

int get12(string s,int p)

{

int i = 0;

int count = s.length();

while((p-i)>=0&&(p+i+1)<count&&s[p-i]==s[p+i+1])

{

i++;

}

return i;

}

};

int main()

{

Solution s;

string t，a;

while(cin>>a){

t = s.longestPalindrome(a);

cout<<t<<endl;}

system("Pause");

return 0;

}