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.HashMap;
import java.util.Map;
import java.util.Scanner;

public class P877B {
	public static void main(String[] args) {

		Scanner s = new Scanner(System.in);

		int n=s.nextInt();
		
		String str=s.next();
		
		Map<String,Integer> map=new HashMap<>();
		
		int max=0;
		
		String res="";
		
		for(int i=1;i<n;i++)
		{
			String sub=str.substring(i-1,i+1);
			System.out.println(sub);
			
			int k=map.getOrDefault(sub,0)+1;
			System.out.println(k);
			
			if(k>max)
			{
				max=k;
				res=sub;
			}
			map.put(sub,k);
		}
		System.out.println(res);
		
	}

}
