import Control.Monad
import Data.Graph
import Data.Bool
import Data.Tuple
import Data.List
import Data.Array
import qualified Data.ByteString.Char8 as B

main :: IO ()
main = do
  [n, m] <- map read . words <$> getLine
  es <- replicateM m $ (\[x, y] -> (x, y)) . map (maybe undefined fst . B.readInt) . B.words <$> B.getLine
  putStrLn . bool "NO" "YES" $ solve n (es ++ map swap es)

solve :: Int -> [(Int, Int)] -> Bool
solve n [] = True
solve n es
  | numOdd == 0 || numOdd == 2 = us == vs
  | otherwise = False
  where
    g = buildG (0, n - 1) es
    numOdd = length . filter odd . elems . outdegree $ g
    vs = map head . group . sort . map fst $ es
    us = sort . reachable g . head $ vs