import Control.Applicative ((<$>))

main :: IO ()
main = getLine >> solve <$> getLine >>= putStrLn

solve :: String -> String
solve "0" = "NO"
solve "1" = "NO"
solve "01" = "NO"
solve "10" = "NO"
solve "101" = "NO"
solve "010" = "NO"
solve _ = "YES"