import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

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

        int chars = Integer.parseInt(br.readLine());


        List<MatrixPoint> charPoints = new ArrayList<>();

        int bestLenght = 1;

        for (int i = 0; i < chars; i++){
            char c = (char)br.read();

            for (MatrixPoint mp:charPoints) {
                mp.insert(c);
                if(mp.checkValid()){
                    if(mp.length > bestLenght){
                        bestLenght = mp.length;
                    }
                }
            }


            MatrixPoint temp = new MatrixPoint();
            temp.insert(c);
            charPoints.add(temp);
        }


        System.out.println(bestLenght);

    }
}
class MatrixPoint{

    public int[] charOccur = new int[20];
    int length = 0;


    public void insert(char c){
        charOccur[c - 'a']++;
        length++;
    }

    public boolean checkValid(){
        int odd = 0;

        for (int i = 0; i < charOccur.length; i++) {
            odd += charOccur[i] % 2 == 1 ? 1 : 0;
        }

        return odd <= 1;
    }

}