main :: IO ()
main = do
 s <- getLine :: IO String 
 print $ fixBatch s
 
fixBatch :: String -> Int
fixBatch xs
  |even $ length xs = 
    let half = length xs `div` 2
      in length $ filter (\t -> fst t /= snd t) $ zip (take half xs) (reverse $ drop half xs)
  |otherwise =  
    let half = length xs `div` 2
      in length $ filter (\t -> fst t /= snd t) $ zip (take half xs) (reverse $ drop (half+1) xs)

