{-# LANGUAGE BangPatterns #-}

import           Control.Monad
import           Control.Monad.State
import           Data.Char
import           Data.Coerce
import qualified Data.ByteString.Char8             as BSC8
import qualified Data.Vector.Fusion.Stream.Monadic as VFSM
import qualified Data.Vector.Unboxed               as VU
import qualified Data.Vector.Unboxed.Mutable       as VUM

main :: IO ()
main = do
  n  <- readLn :: IO Int
  as <- seqInput n
  let s    = (floor :: Double -> Int) . sqrt . fromIntegral . VU.sum $ as
  let _ans = (0 :: Int)
  let _now = (1 :: Int)
  info <- VUM.replicate 2 (0 :: Int)
  rep n $ \i -> do
    if i < s
      then VUM.unsafeModify info succ _now
      else do
        item <- VUM.unsafeRead info _now
        when (item > 0) $ VUM.unsafeModify info pred _now
    now <- VUM.unsafeRead info _now
    VUM.unsafeModify info (+ (max 0 (as VU.! i - now))) _ans
  print =<< VUM.unsafeRead info _ans

type CParser a = StateT BSC8.ByteString Maybe a
runCParser :: CParser a -> BSC8.ByteString -> Maybe (a, BSC8.ByteString)
runCParser = runStateT
{-# INLINE runCParser #-}
int :: CParser Int
int = coerce $ BSC8.readInt . BSC8.dropWhile isSpace
{-# INLINE int #-}
seqInput :: Int -> IO (VU.Vector Int)
seqInput n = VU.unfoldrN n (runCParser int) <$> BSC8.getLine
{-# INLINE seqInput #-}
stream :: Monad m => Int -> Int -> VFSM.Stream m Int
stream !l !r = VFSM.Stream step l
  where
    step x
      | x < r     = return $ VFSM.Yield x (x + 1)
      | otherwise = return $ VFSM.Done
    {-# INLINE [0] step #-}
{-# INLINE [1] stream #-}
rep :: Monad m => Int -> (Int -> m ()) -> m ()
rep n = flip VFSM.mapM_ (stream 0 n)
{-# INLINE rep #-}