main :: IO ()
main = do
  let
    f :: Int -> Int -> Int
    f k m = (2 * k) `min` (m - 1)
  [n, k] <- map read . words <$> getLine :: IO [Int]
  let
    step :: Char -> [Bool] -> [Bool]
    step 'L' rest = False : rest
    step 'R' rest = True : rest
    step _ _ = []
  ds <- foldr step [] <$> getContents :: IO [Bool]
  let
    (m, s) = foldl step (1, 0) . (zipWith (==) <$> id <*> tail) $ ds :: (Int, Int)
      where
        step :: (Int, Int) -> Bool -> (Int, Int)
        step (m, s) b | b         = (m, s + 1)
                      | otherwise = (m + 1, s)
  print $ s + f k m
