/*
 * hehe.cpp
 *
 *  Created on: 2012-12-04
 *      Author:??
 *   ?????????????????
 *???????????????????????????
 *??? abba   cccdeedccc???????
 */
int main(){
	char a[600];
	char b[50][200][50];
	int lena=0;
	cin>>a;
	lena=strlen(a);                                 //??a???
	for(int i=2;i<=lena;i++)
       for(int p=0;p<=lena-i;p++)
       {  for(int j=p;j<p+i;j++)
    		   b[i][p][j]=a[j];                     //b[][][]????????????????????????
    	   int k=p;                                 //?????????
         for( ;k<=p+i/2;k++)
         {   if( b[i][p][k]!=b[i][p][2*p+i-1-k])    //?????????????????????????????????2*p+i-1?
        	   break;
         }
         int judgesame=0;
         for(int j=p;j<i+p&&p>=1;j++)
        	 if(b[i][p-1][j-1]==b[i][p][j])
        		 judgesame++;                       //judgesame?????????????
         if(k==(p+i/2+1)&&judgesame!=i)
         { for(int j=p;j<i+p;j++)
        	      cout<<b[i][p][j];                 //????
            cout<<endl;
         }
       }
	;
	return 0;
}
