"Input" namespace does not exist in Unity.MLAgents.Extensions

I downloaded ML Agents exampels package and imported it to my project and when I did that I got multiple errors. It says that the "Input" namespace does not exist in Unity.MLAgents.Extensions and when I check the code it says "using Unity.MLAgents.Extensions.Input;" but the "Input" part is marked as an error. How do I fix this?

Assets\ML-Agents\Examples\PushBlockWithInput\Scripts\PushBlockWithInputPlayerController.cs(1,33): error CS0234: The type or namespace name 'Input' does not exist in the namespace 'Unity.MLAgents.Extensions' (are you missing an assembly reference?)