Classroom

In a School, there are $N$ students with their roll numbers from $1$ to $N$ and there are $N$ benches for the students. For the examination the sitting arrangement is as follows:- Assume roll number of a student is $X$ then for every student If $X$ $mod$ $2$ $!= 0$ then that student will sit first and then remaining student will sit. Now the teacher wants to know the roll number of the stude