若有以下程序：#include ＜iostream＞using namespace std;class Base{public: Base() { x=0; } int x;};class Derived1: virtual public Base{public: Derived1() {x=10; }};class Derived2: virtual public Base{public: Derived2() { x=20; }};class Derived: public Derived1, protected Derived2{ };int main(){ Derived obj; cout＜＜obj.x＜＜end1; return 0;}该程序运行后的输出结果是 【15】 。