#include<iostream>#include<cstring>#include<set>#include<map>#include<cmath>#include<stack>#include<queue>#include<deque>#include<list>#include<algorithm>#include<stdio.h>#include<iomanip>#define rep(i,n) for(int i=0;i<n;++i)#define fab(i,a,b) for(int i=a;i<=b;++i)#define fba(i,b,a) for(int i=b;i>=a;--i)#define PB push_back#define INF 0x3f3f3f3f#define MP make_pair#define lson l,m,rt<<1#define rson m+1,r,rt<<1|1#define sf scanf#define pf printf#define LL long longconst int N=2105;const int M=2105;using namespace std;typedef pair<int,int>PII;int wa[N],wb[N],wv[N],wd[M];int sa[N],rank[N],height[N];int LEN;int d[N][32];char str[N];int cmp(int *r, int a, int b, int l){      return r[a] == r[b] && r[a+l] == r[b+l];  }  //r数组的长度n从[0,n)//求出的sa为从[1,n]//调用时候r[n-1]=0void da(char *r, int n, int m){          //  倍增算法 r为待匹配数组  n为总长度 m为字符范围      int i, j, p, *x = wa, *y = wb, *t;      for(i = 0; i < m; i ++) wd[i] = 0;      for(i = 0; i < n; i ++) wd[x[i]=r[i]] ++;      for(i = 1; i < m; i ++) wd[i] += wd[i-1];      for(i = n-1; i >= 0; i --) sa[-- wd[x[i]]] = i;      for(j = 1, p = 1; p < n; j *= 2, m = p){          for(p = 0, i = n-j; i < n; i ++) y[p ++] = i;          for(i = 0; i < n; i ++) if(sa[i] >= j) y[p ++] = sa[i] - j;          for(i = 0; i < n; i ++) wv[i] = x[y[i]];          for(i = 0; i < m; i ++) wd[i] = 0;          for(i = 0; i < n; i ++) wd[wv[i]] ++;          for(i = 1; i < m; i ++) wd[i] += wd[i-1];          for(i = n-1; i >= 0; i --) sa[-- wd[wv[i]]] = y[i];          for(t = x, x = y, y = t, p = 1, x[sa[0]] = 0, i = 1; i < n; i ++){              x[sa[i]] = cmp(y, sa[i-1], sa[i], j) ? p - 1: p ++;          }      }  }  // 求出的 height [1,n] 对应sa中的[1,n]// 求出的 rank [0,n-1] 对应sa中的[1,n]// 调用时候最后添加的0不用加进去void calHeight(char *r, int n){           //  求height数组。      int i, j, k = 0;      for(i = 1; i <= n; i ++) rank[sa[i]] = i;      for(i = 0; i < n; height[rank[i++]] = k){          for(k ? k -- : 0, j = sa[rank[i]-1]; r[i+k] == r[j+k]; k ++);      }  }//为了统一，所有的下标从0开始,左闭右开！void fix(int n){    rep(i,n)sa[i]=sa[i+1],rank[i]--,height[i]=height[i+1];}void rmq_init(int n){   rep(i,n)d[i][0]=height[i];   for(int j=1;(1<<j)<=n;j++){       for(int i=0;i+(1<<j)-1<n;i++)           d[i][j]=min(d[i][j-1],d[i+(1<<(j-1))][j-1]);   }} int qurry(int L,int R){    if(L>R)swap(L,R);    L++;    int k=0;    while((1<<(k+1))<=R-L+1)k++;    return min(d[L][k],d[R-(1<<k)+1][k]);}void solve(){   LEN=strlen(str);   str[LEN]=1;   rep(i,LEN)str[LEN+i+1]=str[LEN-i-1];   str[2*LEN+1]=0;   da(str,2*LEN+2,300);   calHeight(str,2*LEN+1);   fix(2*LEN+1);   rmq_init(2*LEN+2);   int n=2*LEN+1;   int ans=1,pos=0;   rep(i,LEN){       int tmp=qurry(rank[i],rank[n-i-1]);       int len=2*tmp-1;       if(len>ans){           ans=len;           pos=i-tmp+1;       }       if(!i)continue;       tmp=qurry(rank[i],rank[n-i]);       len=2*tmp;       if(len>ans){           ans=len;           pos=i-tmp;       }   }   rep(i,ans)putchar(str[i+pos]);puts("");}int main(){    while(~sf("%s",str)){        solve();    }    return 0;}