import Control.Applicative
import Data.ByteString.Char8 (ByteString)
import qualified Data.ByteString.Char8 as B

main :: IO ()
main = solve <$> B.getLine <*> B.getLine >>= print

solve :: ByteString -> ByteString -> Int
solve b1 b2 = sum $ B.zipWith f b1 b2
  where
    f c1 c2 = if c1 == c2 then 0 else 1
