defmodule Main do
  def main do
    ss1 = input(:str)
    ss2 = input(:str)

    len = ss1 |> String.length
    for i <- 0..len - 1 do
        String.at(ss1, i) == String.at(ss2, i)
    end
    |> Enum.count(& &1 == false)
    |> IO.puts
  end

  defp input(type \\ :str) do
    s = IO.gets("") |> String.trim()
    
    case {type, s} do
      {:int, s}  -> s |> String.to_integer()
      {:ints, s} -> s |> String.split("") |> Enum.map(&String.to_integer(&1))
      {:str, s}  -> s
      {:strs, s} -> s |> String.split("")
      _ -> raise "TypeError"
    end
  end
end