import Control.Applicative

getInt :: IO Int
getInt = (\a -> read a :: Int) <$> getLine

getInteger :: IO Integer
getInteger = (\a -> read a :: Integer) <$> getLine

sum_all :: Integer -> Integer
sum_all n = n * (n + 1) `div` 2

main = do
    print =<< sum_all <$> getInteger
