import Control.Applicative
import Data.List

main = do
  d <- read <$> getLine
  [a,b] <- lines <$> getContents
  let x = replicate 14 'x'
      f (i:j:k:t)
        | j>d  = (i+d):(d+k):f (k:t)
        | j<=d = (i+j+k):f (k:t)
      f _ = []
  print $ maximum $ f $ (0:) $ (++[0]) $ map length $ group $ x++a++b++x