import Data.List (sortBy)

main :: IO ()
main = getLine >> solve <$> f >>= print
  where
    f = map read <$> words <$> getLine

solve :: [Int] -> Int
solve = f 0 . sortBy (flip compare)
  where
    f ct [x] = ct + x
    f ct (x:y:ys)
      | x == y + 1 = f ct (y:ys)
      | otherwise = f (ct + x) (y:ys)