import           Control.Monad.State   (StateT(..))
import           Data.Char             (isSpace)
import           Data.Coerce           (coerce)
import qualified Data.ByteString.Char8 as BSC8
import qualified Data.Vector.Unboxed   as VU

main :: IO ()
main = do
  n  <- readLn :: IO Int
  xs <- seqInput n
  print $ VU.foldr' (\x acc -> if x == acc then acc - 1 else acc) n $ xs

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 #-}