isStripe :: Eq a => [a] -> Bool
isStripe [] = True
isStripe (a:[]) = True
isStripe (a:b:[]) = a /= b
isStripe (a:b:c:xs)
	| a == c && a /= b = isStripe (b:c:xs)
	| otherwise = False

main = do
	getLine
	s <- getLine
	
	putStrLn $ if length s <= 3 && isStripe s then "NO" else "YES"