saying that a thing is strange is a relative term.
something strange for you may not be strange for someone else.

You are always welcome with your queries, but this forum strictly discourage any homework assignment where the aim is to get the answer without working hard for it. The proper way of learning is try it yourself first.

Now your hint,

You can use awk for it and use NR field in it.
NR is the current record number on which awk is operating.

Gaurav