Specific question about a VB to C# code snippet

I am currently adding a win-foms addon to my component. It is a settings component where right-clicking the component opens a win forms that allows users to change values.

In my ShowForm() method, I am running into an error, specifically, the red line.

This is a translation I did of the VB code to C#. The original snippet is the following:

Dim param As Parameters.Param_String = DirectCast(Params.Input(0), Parameters.Param_String)

I was wondering what the C#-equivalent of Params.Input(0) is?