let () = 
  Scanf.scanf " %s\n" @@ fun s1 ->
  Scanf.scanf " %s" @@ fun s2 ->
  let lst1 = Str.split (Str.regexp "") s1 in
  let lst2 = Str.split (Str.regexp "") s2 in
  let ans = List.fold_left2
    (fun a b c -> if b = c then a else a + 1) 0 lst1 lst2 in
  Printf.printf "%d" ans
  