using Microsoft.VisualBasic; Microsoft.VisualBasic.Interaction.InputBox(\"Favourite RPG?\", \"Game\", \"Cool!\");
So what this does is basically a
Right click your References in the Solution Explorer click Add Reference,then search for Microsoft.VisualBasic and add it to your references.
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Microsoft.VisualBasic
For more information see this documentation: How to: Add or Remove References By Using the Add Reference Dialog Box