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.Collections;
import java.util.HashMap;
import java.util.Scanner;


public class TwoGram977B {

	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);
		int n = Integer.valueOf(scanner.nextLine());
		String s = scanner.nextLine();

		HashMap<String, Integer> l = new HashMap<>();

		for (int i = 0; i < s.length() - 1; i++) {
			if (l.containsKey(s.substring(i, i + 2))) {
				l.put(s.substring(i, i + 2), (l.get(s.substring(i, i + 2)) + 1) );
			} else {
				l.put(s.substring(i, i + 2), 1);
			}
		}

		System.out.println(Collections.max(l.entrySet(), (entry1, entry2) -> entry1.getValue() - entry2.getValue()).getValue());

	}//main

}