1. Moscow Center of Fundamental and Applied Mathematics, Leninskiye Gory, bld. 1, 119991, Moscow, Russia
2. Lomonosov Moscow State University, Faculty of Mechanics and Mathematics, Leninskiye Gory, bld. 1, 119991, Moscow, Russia
3. Gubkin University, National University of Oil and Gas, Leninsky av. 65, 119991, Moscow, Russia