How to access Unnamed namespace variable nested inside named namespace.?

Consider This Code

namespace apple {   
    namespace {
                 int a=10;
                 int b=10;
              }
   int a=20;
}


int main()
{
cout<<apple::b; //prints 10
cout<<apple::a; // prints 20
}

unnamed namespace "variable a" is always hidden. How to access "variable a" of unnamed namespace.

Is it even legal to declare unnamed namespaces inside named namespaces?