Roll Number System

There are $N$ students in a class and every student want his/her roll number is not divisible by other students roll number. So, now as you are the class teacher (not in real but u can think like a virtual teacher) it is your task to give them roll numbers in such way that the above problem is solved. Find the Roll number of kth student. - $NOTE$ – As the Roll no 1 is topper of the class so the r