N, S = int(input()), input()
if N > 3:
	print("YES")
elif N == 1:
	print("NO")
elif N == 2:
	print("YES" if S[0] == S[1] else "NO")
else:
	prnit("YES" if S[0] == S[1] or S[1] == S[2] else "NO")