import Control.Monad
import Data.Graph
import Data.Array
main = do
  [n,m] <- map read . words <$> getLine
  ls <- replicateM m $ map read . words <$> getLine
  let g = buildG (0,n-1) [p | [a,b] <- ls, p <- [(a,b),(b,a)]]
      v = length $ filter (not . null) $ elems g
      r = length $ reachable g (head $ head ls)
      o = length $ filter (odd . length) $ elems g
  putStrLn $ if v == r && o <= 2 then "YES" else "NO"