When December is incredibly frosty, the famous Dasher and Dancer precede the holiday flight to the Land of Living Skies with a spectacular warm-up. They canter gracefully at a constant rate along a Northern Light Circle of radius 1 km, and curious bear Arctic, an awesome navigator from the Coffee Club Island, periodically records the exact straight-line distance between the reindeers. If the map drawn one morning
is below, find d.

Copyright © December, 2012 by Gregory V. Akulov