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

import qualified Data.Vector.Fusion.Stream.Monadic as VFSM
import qualified Data.Vector.Unboxed.Mutable       as VUM

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 3 n)
{-# INLINE rep #-}

modulo :: Int
modulo = 1_000_000_007
{-# INLINE modulo #-}

main :: IO ()
main = do
  n  <- readLn :: IO Int
  dp <- VUM.unsafeNew (n + 1)
  VUM.unsafeWrite dp 0 (1 :: Int)
  VUM.unsafeWrite dp 1 (2 :: Int)
  VUM.unsafeWrite dp 2 (2 :: Int)
  rep n $ \i -> do
    item1 <- VUM.unsafeRead dp (i - 2)
    item2 <- VUM.unsafeRead dp (i - 3)
    VUM.unsafeWrite dp i (mod (item1 + item2) modulo)
  print =<< VUM.unsafeRead dp (n - 1)