module Main where

import Control.Monad
import Data.List (sort)

main :: IO ()
main = do
    getLine
    xs <- sort . fmap read . words <$> getLine :: IO [Int]
    let bs@(b:_) = zip xs (drop 1 xs)
    let space = uncurry (-) b
    if (space /= 0) && (all (== space) $ fmap (uncurry (-)) bs)
        then putStrLn "YES"
        else putStrLn "NO"