import qualified Data.Text as T
import qualified Data.Text.IO as T
import qualified Data.Text.Read as T

main :: IO ()
main = do
  s <- T.getLine :: IO T.Text
  t <- T.getLine :: IO T.Text
  print . length . filter (uncurry (/=)) $ T.zip s t
 
unsafeTextToInt :: T.Text -> Int
unsafeTextToInt s = case T.signed T.decimal s of
  Right (n, _) -> n
{-# INLINE unsafeTextToInt #-}
