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 = solve <$> (fst . pairs <$> B.getLine) <*> (map pairs . B.lines <$> B.getContents) >>= putStrLn . bool "NO" "YES"

pairs :: B.ByteString -> (Int, Int)
pairs = (\[x, y] -> (x, y)) . map (maybe undefined fst . B.readInt) . B.words

solve :: Int -> [(Int, Int)] -> Bool
solve n es
  | numOdd == 0 || numOdd == 2 = (length . bcc) g <= 1
  | otherwise = False
  where
    g = buildG (0, n - 1) (es ++ map swap es)
    numOdd = length . filter odd . elems . outdegree $ g