#include <iostream>
#include <vector>
using namespace std;
struct out{
    int f;
    int s ;
    int len;
};
out CenterDiscustion(int first,int second, string sub){
    int res = 0 , f1 = first , s1 = second;
    while(f1 >= 0  && sub[f1] == sub[s1]){
        res = s1 - f1 + 1;
        f1--;
        s1++;
    }
    out l {
        f1 + 1, s1 - 1 , res};
    return l ;
}
string StringReturner(string s){
    out len1 , len2 , res{0 , 0 , 0};
    if ( s.length() < 1) return "";
    int f = 0 , se = 0;
    for(int i = 0; i < s.size(); i++){
       len1 = CenterDiscustion(i , i , s);
       len2 = CenterDiscustion(i, i + 1, s);
       if (res.len < len1.len){
           res = len1;
       }
       if (res.len < len2.len){
           res = len2;
       }
    }
    string re = s.substr(res.f , res.len);
    return re;
}
int main() {

    string a = "blll";
    string k = StringReturner(a);
    cout << k;
    return 0;
}