public static Samochod operator -(Samochod s1, Samochod s2)
        {
            Samochod s3 = new Samochod();
            s3.marka = (s1.marka + s2.marka).ToLower();
            s3.predkosc = s1.predkosc - s2.predkosc;
            return s3;
        }