import Data.List
import Control.Monad

day :: [String]
day = ["SUN", "MON", "TUE", "WED", "WED", "THU", "FRI", "SAT"]

main = print =<< ((pure (\n -> div (n * (n + 1)) 2)) <*> getInt)

getInt :: IO Int 
getInt = (pure read) <*> getLine
