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")