import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int n = sc.nextInt();
        char[] arr = sc.next().toCharArray();
        boolean can;
        if (n == 1) {
            can = false;
        } else if (n == 2) {
            can = (arr[0] == arr[1]);
        } else if (n == 3) {
            can = (arr[0] == arr[1] || arr[1] == arr[2]);
        } else {
            can = true;
        }
        if (can) {
            System.out.println("YES");
        } else {
            System.out.println("NO");
        }
    }
}