def main()
  n = gets.chomp.to_i
  a = gets.chomp.strip
  b = gets.chomp.strip
  c = gets.chomp.strip
  count = 0
  for i in 0..(n-1) do
    if ((a[i] == b[i]) && (b[i] == c[i]))
      next;
    elsif ((a[i] == b[i]) || (b[i] == c[i]) || (c[i] == a[i]))
      count += 1
    else
      count += 2
    end
  end
  puts "#{count}"
end
main