1. Faculty of Computer Science, Goce Delčev University, Goce Delčev 89, 2000 Štip, Macedonia
2. Department of Mathematics and Informatics, Faculty of Science and Mathematics, University of Niš, Višegradska 33, 18000 Niš, Serbia
3. Department of Systems Analysis and Operations Research, Reshetnev University, Prosp. Krasnoyarskiy Rabochiy 31, Krasnoyarsk 660037, Russia