若有以下程序：
#include ＜iostream＞
using namespace std;
class Basepublic:
Base()
x=0;
int x;
;
class Derived1: virtual public Basepublic:
Derived1()
x=10;
;
class Derived2: virtual public Basepublic:
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】 。