{-# LANGUAGE BangPatterns       #-}
{-# LANGUAGE NumericUnderscores #-}

import           Control.Monad
import           Control.Monad.Cont
import           Data.IORef
import qualified Data.Vector.Fusion.Stream.Monadic as VFSM

zeta :: Int -> Int -> IO Double
zeta a x = do
  res <- newIORef (a - 1)
  withBreak $ \break -> do
    rep (x - 1) $ \_ -> do
      liftIO $ modifyIORef res (* a)
      ret <- liftIO $ readIORef res
      when (ret > 1_000_000_000_000) $ break ()
  d <- readIORef res
  return (1.0 / fromIntegral d)

stream :: Monad m => Int -> Int -> VFSM.Stream m Int
stream !l !r = VFSM.Stream step l
  where
    step x
      | x < r     = return $ VFSM.Yield x (x + 1)
      | otherwise = return $ VFSM.Done
    {-# INLINE [0] step #-}
{-# INLINE [1] stream #-}

rep :: Monad m => Int -> (Int -> m ()) -> m ()
rep n = flip VFSM.mapM_ (stream 0 n)
{-# INLINE rep #-}

rep2 :: Monad m => (Int -> m ()) -> m ()
rep2 = flip VFSM.mapM_ (stream 2 1_000_000)

withBreak :: ((r -> ContT r IO b) -> ContT r IO r) -> IO r
withBreak = flip runContT pure . callCC
{-# INLINE withBreak #-}

main :: IO ()
main = do
  x <- readLn :: IO Int
  if x == 2 then putStrLn "1000000"
  else do
    res <- newIORef (0.0 :: Double)
    rep2 $ \a -> do
      d <- zeta a x
      modifyIORef' res (+ d)
    print . floor . (* 1000000) =<< readIORef res