import Control.Applicative
import Control.Monad
import Data.List

solve :: Int -> [Int] -> Int
solve c ai = head $ f c (sortBy (flip compare) ai) 0 ++ [-1]
    where
        f rest [] ans = do
            guard (rest == 0)
            return ans
        f rest (x:xs) ans = do
            let m = rest `div` x
            i <- [m,m-1..0]
            f (rest - i*x) xs (ans + i)

main :: IO ()
main = do
    c <- readLn :: IO Int
    n <- readLn :: IO Int
    ai <- map read . words <$> getLine :: IO [Int]
    print $ solve c ai