import java.util.*;
import java.io.*;

public class Main {
    public static void main(String[] args) throws Exception {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        int n = Integer.parseInt(br.readLine());
        char[] arr = br.readLine().toCharArray();
        for (int i = 1; i < arr.length; i++) {
            if (arr[i] == arr[i - 1]) {
                System.out.println("YES");
                return;
            }
        }
        if (arr.length >= 4) {
            System.out.println("YES");
        } else {
            System.out.println("NO");
        }
    }
}