import Control.Applicative ((<$>), (<*>))
import Control.Monad (guard)
import Data.List (foldl')
import Data.Vector.Unboxed (Vector, (!), (//))
import qualified Data.Vector.Unboxed as V

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

solve :: Int -> Int -> Double
solve n k = sum $ do
  ti <- [0 .. 6*n]
  ji <- [0 .. 6*n]
  guard $ ti > ji
  return $ dpt ! ti * dpj ! ji
  where dpt = foldl' f ((V.replicate (6*n+1) 0) // [(0,1.0)]) ((replicate (n-k) l1) ++ (replicate k l2))
        dpj = foldl' f ((V.replicate (6*n+1) 0) // [(0,1.0)]) (replicate n l1)
        f dp ds = V.accum (+) (V.replicate (6*n+1) 0) $ do
          (v, p) <- ds
          i <- [0..6*n]
          guard $ i >= v
          return (i, dp ! (i-v) / p)

l1 = [(1,6.0),(2,6.0),(3,6.0),(4,6.0),(5,6.0),(6,6.0)] :: [(Int,Double)]
l2 = [(4,3.0),(5,3.0),(6,3.0)] :: [(Int,Double)]