At OIM University $($OIMU$),$ there are two main categories of students: recent high school graduates and transfer students from other universities. On average, recent high school graduates spend $4$ years at the university before graduating, whereas transfer students typically complete their studies in $2$ years. Among the students admitted to the university, $20\%$ are transfer students. Considering that the university admits an annual average of $8,000$ students, what is the total number of students enrolled at any given time on average?