After having collected samples along the shore all day long, a marine biologist walks back to her campsite, 2.85 km...

After having collected samples along the shore all day long, a marine biologist walks back to her campsite, 2.85 km away. Her dog runs ahead, at twice the speed, reaches the campground and turns around until it meets her again. Then, the dog proceeds to run back to the campground again. This continues until the marine biologist reaches her campground. What distance did the dog run? (use km as units)