import Control.Applicative ((<$>))
import Data.List

import Data.Char (isSpace)
import Data.ByteString.Char8 (ByteString)
import qualified Data.ByteString.Char8 as B

main :: IO ()
main = do
  B.getLine
  solve <$> readIntList >>= putStrLn

solve :: [Int] -> String
solve xs = let sxs = sort xs in f $ zipWith (-) (tail sxs) sxs
  where
    f (y:ys) = if (y > 0) && all (== y) ys then "YES" else "NO"

readIntList :: IO [Int]
readIntList = unfoldr f <$> B.getLine
  where
    f s = do
      (n, s') <- B.readInt s
      return (n, B.dropWhile isSpace s')