The little prince (the main character of the novel written by Antoine de Saint-Exupery) lives on the spherical planet named B-612,the density of which is 5200 kg/${\mathrm{m}}^3$. The Little Prince noticed that if he quickens his pace, he feels himself lighter. When he reached the speed of 2 m/s he became weightless, and began to orbit about the planet as a satellite. What is escape speed on the surface of planet?