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

public class No290 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int n = sc.nextInt();
		int mae = 2;
		String s = sc.next();
		for(int i = 0; i < n; i++) {
			int t = s.charAt(i);
			if(mae == t) {
				System.out.println("YES");
				return;
			}
			mae = t;
		}
		System.out.println("NO");
	}
}