{-# LANGUAGE BangPatterns #-}

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

main :: IO ()
main = do
  [h, a, d] <- map (read :: String -> Int) . words <$> getLine
  dp <- VUM.unsafeNew 10101
  rep (h + 1) $ \i -> VUM.unsafeWrite dp i (0 :: Double)
  rep1 h $ \i -> do
    let
      preA = max (0 :: Int) (i - a)
      preD = max (0 :: Int) (i - d)
    item1 <- VUM.unsafeRead dp preA
    item2 <- VUM.unsafeRead dp preD
    VUM.unsafeWrite dp i (min (item1 + 1.0) (item2 + 1.5))
  print =<< VUM.unsafeRead dp h

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 #-}

rep1 :: Monad m => Int -> (Int -> m ()) -> m ()
rep1 n = flip VFSM.mapM_ (stream 1 (n + 1))
{-# INLINE rep1 #-}