15
MIRZOYANOVECLOX
 23
AABBBAAACCCCCAAADDDDDDD
 2
QA
 11
GGRRAATTZZZ
 6
AZAZAZ
 10
SQSQSQSQTG
 3
KEK
 100
URXCAIZFIBNJTPCZHBQIBCILLPXZCFGMKKZMNPLCYGAVJVIBMCZEBSJWPSCPQDYCTTKPOKIJRSKIZPDGCHVOUTMPNECYORSFZFNC
 3
LOL
 2
WW
 8
PUTINVOR
 26
QWERTYUIOPASDFGHJKLZXCVBNM
 5
AZAZA
 9
EGORLETOV
 7
KADUROV
 9
MIKEPIDOR
 9
AAAAAAAAA
 100
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA
 5
FUFEL
 50
NYQAHBYYOXLTRYQDMVENEMAQNBAKGLGQOLXNAIFNQTOCLNNQIA

MI
 DD
 QA
 ZZ
 AZ
 SQ
 KE
 IB
 LO
 WW
 PU
 QW
 AZ
 EG
 KA
 MI
 AA
 AA
 FU
 YQ

import java.util.Arrays;
import java.util.Scanner;

public class Dk{
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        String str=sc.next();
        String[] arr=new String[str.length()-1];
        for (int i = 0; i < str.length()-1; i++) {
            arr[i]=""+str.charAt(i)+str.charAt(i+1)+"";
        }
        Arrays.sort(arr);
        for (int i = 0; i < arr.length; i++) {
            System.out.println(arr[i]);
        }
        int count=1,big=-1;
        String ans="";
        for (int i = 0; i < arr.length-1; i++) {
            if (arr[i].equals(arr[i+1])) {
                count++;
            }
            
                if (big<count) {
                    big=count;
                    count=1;
                    ans=arr[i];
                }
        }
        System.out.println("ans "+ans);
    }
}