I want to reduce the number of `Vertices` of a circle but I cannot find out the input box for setting this. I am now at the `Edit Mode` and already selected a circle. Where is the input box?

[![enter image description here](https://i.stack.imgur.com/O2PPb.png)](https://i.stack.imgur.com/O2PPb.png) [![enter image description here](https://i.stack.imgur.com/EipXP.png)](https://i.stack.imgur.com/EipXP.png)