using System;

​

​

public class Foo{

    public int A;

    private int B;

    public Foo(){}

    public Foo(int a, int b){

        A=a;

        B=b;

    }

    public static Foo Add(Foo f1, Foo f2 ){

        int a =f1.A+f2.A;

        int b = f1.B+f2.B;

        return new Foo{

            A= a,

            B=b

        };

    }

    public Foo Clone(Foo proto){

        return new Foo(proto.A, proto.B);

    }

    public override string ToString(){

        return "A= " + A + " B= " + B;

    }

}

​

public class Program

{

    public static void Main()

    {

        var f1 =new Foo(1,-1);

        var f2 =new Foo(2,-2);

        var f3 =Foo.Add(f1,f2);

        Console.WriteLine(f3);

        var f4 = new Foo();

        Console.WriteLine(f4.Clone(f3));

    }

}