1. School of Science, Hainan University, Haikou, Hainan, 570228, P.R. China
2. Department of Applied Mathematics and Computer Science, Belarusian State University, Minsk 220030, Belarus.
3. Department of Mathematics and Technologies of Programming, Francisk Skorina Gomel State University, Gomel 246019, Belarus
4. School of Science, Hainan University, Haikou, Hainan, 570228, P.R. China.