import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.HashMap;

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

        int max = 0;
        int currentCount = days;

        while(true) {
            int oddCount = 0;
            HashMap<Character, Integer> map = new HashMap<>();
            int start = 0;
            /*for (int j = 0; j < currentCount; j++) {
                char x = brands.charAt(i+j);
                map.putIfAbsent(x, 0);
                int y = map.get(x);
                if (y%2==0){
                    oddCount++;
                }
                map.put(x, y+1);
            }*/
            for (int i = 0; i < currentCount; i++) {
                char x = brands.charAt(i);
                map.putIfAbsent(x, 0);
                int y = map.get(x);
                if (y%2==0){
                    oddCount++;
                } else oddCount--;
                map.put(x, y+1);
            }
            if (oddCount<=1){
                System.out.println(currentCount);
                System.exit(0);
            } else {
                for (int j = 1; j < days - currentCount; j++) { // mozna +1
                    char x = brands.charAt(j-1);
                    if (map.get(x) % 2 == 0) {
                        oddCount++;
                    } else oddCount--;
                    map.put(brands.charAt(j-1), map.get(x)-1);

                    char y = brands.charAt(j+currentCount-1);
                    map.putIfAbsent(y, 0);
                    if (map.get(y)%2 ==0) {
                        oddCount++;
                    } else oddCount--;
                    map.put(y, map.get(y)+1);
                    if (oddCount<=1) {
                        System.out.println(currentCount);
                        System.exit(0);
                    }
                }

            }
            currentCount--;
        }
    }
}