import Control.Applicative

main :: IO ()
main = do
  n <- read <$> getLine
  s <- getLine
  print $ if solve n s then "YES" else "NO"

solve :: Int -> String -> Bool
solve n s
  | length s > 3 = True
  | length s == 1 = False
  | s `elem`  ["01", "10", "010", "101"] = False
  | otherwise = True