import Control.Applicative ((<$>))
import Data.List (unfoldr)

main :: IO ()
main = solve <$> readLn >>= print

solve :: Int -> Int
solve n = sum . takeWhile (<=n) $ pns

pns :: [Int]
pns = 2 : unfoldr f 3
  where isPn x = all ((/=0) . (mod x)) $ takeWhile ((<=x) . (^2)) pns
        f x | isPn x = Just (x, x+2)
            | otherwise = f (x+2)