import Control.Applicative
import Control.Monad
import Control.Monad.ST
import Debug.Trace
import Data.List hiding (insert)
import Data.Array
import Data.Set (Set, fromList, toList, insert, member, empty)
import qualified Data.Set as S
import Data.Array.ST

main :: IO ()
main = solve <$> (map read . words <$> getLine) <*> (map (map read . words) . lines <$> getContents) >>= putStrLn . yesno

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

solve :: [Int] -> [[Int]] -> Bool
solve [n, m] [] = True
solve [n, m] g = let deg = (map length . group . sort . concat) g
                 in if (all even) deg || (length . filter odd) deg == 2
                      then let reachable = toList $ dfs ((head . head) g) S.empty (toArray n g)
                           in (sort . nub) reachable == (sort . nub . concat) g
                      else False

toArray :: Int -> [[Int]] -> Array Int [Int]
toArray n es = runST $ do
  g <- newArray (0, n-1) [] :: ST s (STArray s Int [Int])
  forM_ es $ \[x, y] -> do
    readArray g x >>= writeArray g x . (y:)
    readArray g y >>= writeArray g y . (x:)
  freeze g

dfs :: Int -> Set Int -> Array Int [Int] -> Set Int
dfs u vis g = foldl' f (insert u vis) (g ! u)
  where
    f :: Set Int -> Int -> Set Int
    f vis v
      | member v vis = vis
      | otherwise  = dfs v vis g