Set Filter in Lookup field problem

Set Filter in Lookup field problem

Goodevening.

I am trying to create dynamic lookup exactly like the example. I created a form called Country with a textfield to add the countries and a form called State with a Country lookup field and State Name as text field. I also did a form called Main which contains the lookup fields Country and State. When I am trying to add the set filter in State lookup then it is not possible to write Country == input.Country (as the example says). From the criteria it only accepts ((Country.Country == "input.Country")) which does not work. What is wrong? Is there any way to write a filter manually without opens this pop up window with the criterias?