-- yukicoder My Practice
-- author: Leonardone @ NEETSDKASU

import Data.List (sort)

main = putStrLn . solve . sort . map read . tail . words =<< getContents

solve xs = ans where
    ys = sort . map (\(a, b) -> a - b) $ tail xs `zip` xs
    hd = head ys
    ed = head $ reverse ys
    ans = if hd > 0 && hd == ed then "YES" else "NO"