import Data.Graph
import Data.Bool
import Data.Array

main :: IO ()
main = solve <$> (read . head . words <$> getLine) <*> (map (map read . words) . lines <$> getContents) >>= putStrLn . bool "NO" "YES"

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