import Control.Monad (replicateM)
import Data.List

main = do
  [n, m] <- getInts
  r <- judge . concat <$> replicateM m getInts
  putStrLn (yesno r)

getInts :: IO [Int]
getInts = map read . words <$> getLine

judge :: [Int] -> Bool
judge = (\x -> x == 0 || x == 2) . count odd . map length . group . sort

count :: (a -> Bool) -> [a] -> Int
count p = length . filter p

yesno :: Bool -> String
yesno True  = "YES"
yesno False = "NO"