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Marija Paunovic
Department of Natural Science,
University of Kragujevac, Faculty of Hotel Management and Tourism,
Department of Computer Science,
University MB, Faculty of Business and LawVrnjacka Banja,Belgrade
Babak Mohammadi
Department of Mathematics, Marand Branch,
Islamic Azad UniversityMarand, Iran
Vahid Parvaneh
Department of Mathematics, Gilan-E-Gharb Branch,
Islamic Azad UniversityGilan-E-Gharb, Iran