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

public class Abb {

    public static void main(String[] args) {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int a, b, c , d;
        String pattern;
        int len;

        try {
            String[] line = br.readLine().split("\\s+");
            a = Integer.parseInt(line[0]);

            pattern = br.readLine();
            int j, i;
            //Najit stred
            boolean found = false;
            for (i = pattern.length()-1; i >= 0; i--) {
                for (j = i - 1; j >= 0; j--) {
                    if (pattern.charAt(i) == pattern.charAt(j)) {
                        System.out.println(j);
                        return;
                    }
                }

                if (found == false) {
                    System.out.println(i);
                    return;
                }
            }



            //spocist vzdalenost od stredu
        }
        catch (IOException e) {
            e.printStackTrace();
        }
    }
}