import Control.Applicative ((<$>), (<*>))
import Control.Monad
import Data.List

main :: IO ()
main = do
  solve <$> getl toInt >>= print

solve :: Int -> Int
solve n = n * (n+1) `div` 2

toInt :: String -> Int
toInt = read

getl :: (String -> a) -> IO a
getl f = f <$> getLine
