Suppose We Have the Following Namespace

Suppose we have the following namespace:
namespace A
{
void f(int);
//...
}
using namespace A;
// In the global namespace
void g()
{
f('a');// calls A::f(int)
}
In the global namespace,the function g( )calls f('a').There is no problem here,f('a')is unambiguously A::f(int).Now suppose at some later time,the following namespace grouping and using directive is inserted prior to the call to function f.
namespace B
{
void f(char);
//...
}
using namespace B;
For convenience,all these are listed again.
namespace A
{
void f(int);
//...
}
using namespace A;
namespace B
{
void f(char);
//...
}
using namespace B;
// In the global namespace
void g()
{
f('a');
}
In g(),to what does the call,f('a')resolve? How could the code be modified so that the call still resolves to A::f(int)?