import Data.List
import qualified Data.Set as Set
import Data.Char
import Data.Maybe
import Control.Monad
import qualified Data.ByteString.Char8 as BS8

main=do
    n <- fst . fromJust . BS8.readInt <$> BS8.getLine
    a <- unfoldr (BS8.readInteger . BS8.dropWhile isSpace) <$> BS8.getLine
    
    let s = foldl (\a b->Set.insert b a) (Set.empty) a
        ans = if Set.size s == n then "YES" else "NO"
    
    putStrLn ans
