Input

Output

Sample

Kazak

aza

 #include <iostream>

 #include <cstdio>

 #include <cstring>

 #include <algorithm>

 #include <vector>

 #include <cmath>

 #include <queue>

 #include <stack>

 #include <map>

 #include <string>

 #include <set>

 using namespace std;

 typedef long long LL;

 const int INF = 2e9;

 const LL LNF = 9e18;

 const int MOD = 1e9+;

 const int MAXN = 1e4+;

 bool cmp(int *r, int a, int b, int l)

 {

     return r[a]==r[b] && r[a+l]==r[b+l];

 }

 int r[MAXN], sa[MAXN], Rank[MAXN], height[MAXN];

 int t1[MAXN], t2[MAXN], c[MAXN];

 void DA(int str[], int sa[], int Rank[], int height[], int n, int m)

 {

     n++;

     int i, j, p, *x = t1, *y = t2;

     for(i = ; i<m; i++) c[i] = ;

     for(i = ; i<n; i++) c[x[i] = str[i]]++;

     for(i = ; i<m; i++) c[i] += c[i-];

     for(i = n-; i>=; i--) sa[--c[x[i]]] = i;

     for(j = ; j<=n; j <<= )

     {

         p = ;

         for(i = n-j; i<n; i++) y[p++] = i;

         for(i = ; i<n; i++) if(sa[i]>=j) y[p++] = sa[i]-j;

         for(i = ; i<m; i++) c[i] = ;

         for(i = ; i<n; i++) c[x[y[i]]]++;

         for(i = ; i<m; i++) c[i] += c[i-];

         for(i = n-; i>=; i--) sa[--c[x[y[i]]]] = y[i];

         swap(x, y);

         p = ; x[sa[]] = ;

         for(i = ; i<n; i++)

             x[sa[i]] = cmp(y, sa[i-], sa[i], j)?p-:p++;

         if(p>=n) break;

         m = p;

     }

     int k = ;

     n--;

     for(i = ; i<=n; i++) Rank[sa[i]] = i;

     for(i = ; i<n; i++)

     {

         if(k) k--;

         j = sa[Rank[i]-];

         while(str[i+k]==str[j+k]) k++;

         height[Rank[i]] = k;

     }

 }

 int dp[MAXN][], mm[MAXN];

 void initRMQ(int n, int b[])

 {

     mm[] = -;

     for(int i = ; i<=n; i++)

         dp[i][] = b[i], mm[i] = ((i&(i-))==)?mm[i-]+:mm[i-];

     for(int j = ; j<=mm[n]; j++)

     for(int i = ; i+(<<j)-<=n; i++)

         dp[i][j] = min(dp[i][j-], dp[i+(<<(j-))][j-]);

 }

 int RMQ(int x, int y)

 {

     if(x>y) swap(x, y);

     x++;

     int k = mm[y-x+];

     return min(dp[x][k], dp[y-(<<k)+][k]);

 }

 char str[MAXN];

 int main()

 {

     scanf("%s" ,str);

     int len = strlen(str);

     int n = *len+;

     for(int i = ; i<len; i++)

         r[i] = r[n--i] = str[i];

     r[len] = '$'; r[n] = ;

     DA(r, sa, Rank, height, n, );

     initRMQ(n, height);

     int st, ans = , lcp;

     for(int i = ; i<len; i++)

     {

         lcp = RMQ(Rank[i], Rank[n--i]);   //奇数，以i为中点匹配

         if(*lcp->ans)

             ans = *lcp-, st = i-lcp+;

         if(i==) continue;

         lcp = RMQ(Rank[i], Rank[n-i]);  //偶数， 逆串往后退一个位置进行匹配

         if(*lcp>ans)

             ans = *lcp, st = i-lcp;

     }

     for(int i = st; i<st+ans; i++)

         putchar(str[i]);

     putchar('\n');

 }