import Control.Applicative
import Control.Monad
import qualified Data.ByteString.Char8 as B
import Data.Maybe (fromJust)
import Text.Printf
import Debug.Trace

readInts :: B.ByteString -> [Int]
readInts = map (fst . fromJust . B.readInt) . B.words

getInts :: IO [Int]
getInts = liftM readInts B.getLine

solve :: Int -> Int -> Int
solve n k = if k > 1
            then 2^(n - k)
            else (2^(n - 1) - n)

main = do
  [n,k] <- getInts
  print $ solve n k