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】 。