import Control.Applicative
import Data.List

solve l ws = subtract 1 $ length $ unfoldr go (l,ws) where
  go (0,[]) = Just (0, (-1,[]))
  go (_,[]) = Nothing
  go (m,x:xs)
    | m >= 0 = Just (m, (m-x,xs))
    | otherwise = Nothing

main = do
  l <- (read :: String -> Int) <$> getLine
  n <- getLine
  ws <- fmap (read :: String -> Int) . words <$> getLine
  print $ solve l $ sort ws