import Control.Applicative ((<$>))
import Data.IntSet (IntSet)
import qualified Data.IntSet as IS

main :: IO ()
main = solve <$> map read <$> words <$> getLine >>= print

solve :: [Int] -> Int
solve [n, d] = f IS.empty 0 0
  where f st pc os | IS.member os st = pc - 1
                   | otherwise = f (IS.insert os st) (pc + k + 1) ((os + d * (k + 1)) `mod` n)
          where k = (n - 1 - os) `div` n