readDigits :: IO [Int]
readDigits = map read <$> words <$> getLine

main :: IO ()
main = do
    [l,k] <- readDigits
    let ls = [l,(l-k)..0]
    putStrLn . show $ go k [n | n<-ls, n>k]
    where
    go _ [] = 0
    go _ (_:[]) = 0
    go k (a:b:xs) = k + go k xs