defmodule Main do
  def main do
    1..3
    |> Enum.map(fn _ ->
      IO.read(:line)
      |> String.trim()
    end)
    |> solve
    |> IO.puts()
  end

  def solve([n, s, t]) do
    0..((n |> String.to_integer()) - 1)
    |> Enum.count(fn i ->
      s |> String.to_charlist() |> Enum.at(i) !=
        t |> String.to_charlist() |> Enum.at(i)
    end)
  end
end