import Control.Monad
import Data.List
import Data.Maybe
import qualified Data.ByteString.Char8 as BS
import Data.Time
import Data.Time.Calendar
import Data.Char

tuplify2 (x:y:_) = (x,y)
tuplify2 _ = undefined

--Input functions with ByteString
readInt = fst . fromJust . BS.readInteger
readIntTuple = tuplify2 . map readInt . BS.words
readIntList = map readInt . BS.words

getInt = readInt <$> BS.getLine
getIntList = readIntList <$> BS.getLine
getIntNList n = map readIntList <$> replicateM (fromIntegral n) BS.getLine
getIntMatrix = map readIntList . BS.lines <$> BS.getContents
getIntTuple = readIntTuple <$> BS.getLine
getIntNTuples n = map readIntTuple <$> replicateM (fromIntegral n) BS.getLine
getIntTuples = map readIntTuple . BS.lines <$> BS.getContents

p :: (Show a)=>a->IO ()
p=putStrLn.show
ps=putStrLn

main=do
    [l,k]<-map (read::String->Int).words<$>getLine
    let (d,m)=divMod l (2*k)
    putStrLn.show$(if (m==0) then (d-1)*k else d*k)