double hmean(double a, double b) {
if (a == -b )
throw runtime_error("Runtime error occurred");
return 2.0*a*b/(a + b);
}

int main() {
double x = 10;
double y = -10;

try {
int result = hmean(x, y);
cout << "hmean: " << result << endl;
}
catch (const runtime_error& e) {
cout << "Caught: " << e.what() << endl;
} catch (...) {
cout << "Caught an unknown exception." << endl;
}
return 0;
}