using System;

public class Program

{

    public static void Main()

    {

        Console.WriteLine(Foo.x);

        var a = new Foo();

        a.Hi();

        Foo.x = 1;

        a.Hi();

        a.Bump();

        a.Hi();

    }

}

​

​

public class Foo

{

    public static int x { get; set; } = 0;

    public void Hi() => Console.WriteLine(x);

    public void Bump() => x = x + 1;

}