C++ Hello World issue

I am trying to solve the C++ Hello World exercise in the online editor but it says the tests timed out.
I am using the following code:
#include “hello_world.h”

using namespace std;

namespace hello_world {

string hello() { return “Hello, World!”; }

} // namespace hello_world

And receiving the following error:
Your tests timed out. This might mean that there was an issue in our infrastructure, but more likely it suggests that your code is running slowly. Is there an infinite loop or something similar?

Please check your code, and if nothing seems to be wrong, try running the tests again.

The was a backlog due to a DDoS. You may want to try again in a few minutes.