FRANKFURT (Reuters) - Volkswagen reported an 18.6 percent drop in third-quarter adjusted operating profit to 3.51 billion euros (3.12 billion pounds), weighed down by weaker vehicle sales and headwinds tied to the introduction of more stringent anti-pollution rules. It affirmed on Tuesday its target for 2018 operating return on sales before special items at both the group and its passenger cars business area to come to 6.5 to 7.5 percent.But including special items, the figure will fall..