/**
 *file:????11-24??
 *author:???
 *date?201011-26
 *discription?????
 */
int main ()
{
	//????????????????i??????j,k,m?????l?????len???????
	char str[501] ;
	int i , j , k , l , m , len ;
	cin >> str ;
	len = strlen( str ) ;
	for ( i = 2 ; i <= len ; i ++ )//????????????????
	{
		for ( j = 0 ; j <= len - i ; j ++ )//?????????
		{
			l = j + i / 2 ;//l??????????
			//??????????????????????????????
			for ( k = j ; k <= l ; k ++ )
			{
				if ( str[k] != str[2*j+i-k-1] ) break ;
			}
			//?????????????????????????????????????????????
			if ( k == l+1 )
			{
				for ( m = j ; m < j + i ; m ++ )
					cout << str[m] ;
				cout << endl ;
			}
		}
	}
	return 0 ;
}