n = int(raw_input())
s = raw_input()
ans = "NO"
for i in range(n):
	for j in range(i+1,n-i):
		k = i+j
		print s[i:k], s[k:k+j]
		if s[i:k] == s[k:k+j]:
			ans = "YES"
			break
	if ans == "YES":break		
print ans