import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.Scanner;

public class Mugs {
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int L = Integer.parseInt(br.readLine());


        char[] list = br.readLine().toCharArray();
        int right[] = new int[L];

        int map[] = new int[L];
        for (int i = 0; i < L; i++) {
            int c = list[i] - 'a';
            map[i] = 1 << c;
        }

        right[L-1] = map[L-1];
        for (int i = L-2; i >= 0; i--) {
            right[i] = right[i+1] ^ map[i];
//            System.out.printf("RIGHT: %d - %s\n", i,Integer.toString(right[i], 2));
        }

        for (int length = L; length >= 0; length--) {
            if (length != L && length%2 == 0) {
                continue;
            }
            int minBitCount = Integer.MAX_VALUE;
            for (int j = 0; j < L-length+1; j++) {
                int diff;
                if (j < L-length) {
                    diff = right[j+length] ^ right[j];
                }
                else {
                    diff = right[j];
                }

//                System.out.printf("%d:%d - %s\n", i,j,Integer.toString(diff, 2));
                int bitCount = Integer.bitCount(diff);
                if (bitCount <= 1) {
                    System.out.println(length);
                    return;
                }
                if (bitCount < minBitCount) {
                    minBitCount = bitCount;
                }
            }

            if (minBitCount > 2) {
                length -= (minBitCount-2);
            }
        }

    }

}