using System;

public class Program

{

    public class Foo {

        public int Increment() {

            return IncrementInternal.Increment();

        }

        private static class IncrementInternal {

            private static int counter = 0;

            public static int Increment() {

                return counter++;

            }

        }

    }

    public static void Main()

    {

        var foo = new Foo();

        Console.WriteLine(foo.Increment());

        Console.WriteLine(foo.Increment());

        Console.WriteLine(foo.Increment());

        var foo2 = new Foo();

        Console.WriteLine(foo2.Increment());

        Console.WriteLine(foo2.Increment());

        Console.WriteLine(foo2.Increment());

    }

}