How to enable users to insert an infinity number

I am designing a web page which give admin users the opportunity to manage the users below them. in one section of this admin page, the admin user is required to fill out how many queries he permits to each user below him to run in this system (i.e. queries limit).

This input looks like this:

The admin can enter a number in this box, increase it or decrease it.

The problem is: the admin should have an option to permit the user to run an infinity queries, i.e. not limit the number of queries he can run.

It should look something like this:

How can I manage allow the users to enter an infinity number, in an efficient and clean way?