#include "iostream"
#include "string"
#include "vector"
using namespace std;
bool is_palindrom (string s,int nach,int krai) {
for (int i=nach,j=krai;i<=j;i++,j--) if (s[i]!=s[j]) return false;
return true;
}
int main () {
char ch;
string s,s1,spal;
int j=-1,mx=-1;
while (cin>>ch) {
s+=ch;
j++;
int i=-1;
string s1=s;
vector<int>a;
do {
i++;
if (s1[i]==ch) a.push_back(i);
}
while (i<=s1.length());
for (int i=0;i<a.size();i++)
if (is_palindrom(s1,a[i],j)) {
string s2=s1.substr(a[i],j-a[i]+1);
int l=s2.length();
if (l>mx) {mx=l;spal=s2;break;}
}
}
cout<<spal<<endl;
system ("pause");
return 0;
}
