def main():
	n, s = int(input()), input()
	
	if n > 3:
		print("YES")
	elif n > 1:
		for i in range(n-1):
			if s[i] == s[i+1]:
				print("YES")
				break
		else:
			print("NO")
	else:
		print("NO")
		
		
if __name__ == "__main__":
	main()