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

public class Mugs {
    int n;
    final int letters = 20;
    boolean count[][];

    private void setUp() throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        n = Integer.parseInt(br.readLine());
        String line = br.readLine();

        count = new boolean[letters][n];
        count[line.charAt(0) - 'a'][0] = true;
        for (int i = 1; i < n; ++i) {
            char c = line.charAt(i);
            for (int j = 0; j < letters; ++j) {
                count[j][i] = count[j][i - 1];
            }
            count[c - 'a'][i] = !count[c - 'a'][i];
        }
    }

    public int solve() throws Exception {
        setUp();

        for (int i = n-1; i > 0; --i) {
            for (int j = i; j < n; ++j) {
                boolean seq[] = getInterval(j - i, j);
                int odd = 0;
                for (int k = 0; k < letters; ++k) {
                    if (seq[k]) {
                        odd++;
                    }
                }
                if ((i + 1) % 2 == 0) {
                    // even
                    if (odd == 0) { //ok
                        return i+1;
                    }
                } else {
                    // odd
                    if (odd == 1) { //ok
                        return i+1;
                    }
                }
                if (odd > 3) {
                    i -= odd-4;
                    break;
                }
            }
        }
        return 1;
    }

    private boolean[] getInterval(int a, int b) {
        boolean tmp[] = new boolean[letters];
        for (int i = 0; i < letters; ++i) {
            tmp[i] = count[i][b];
            if (a > 0) {
                tmp[i] = (tmp[i] == count[i][a-1] ? false : true);
            }
        }
        return tmp;
        //ghjahjghsajdjhlfslja
    }

    public static void main(String[] args) throws Exception {
        Mugs m = new Mugs();
        System.out.println(m.solve());
    }
}