Where should the configuration file be located?

The following code is part of the camera calibration program in OpenCV. But I get an error when the program starts: it says

Could not open configuration file.

I put the configuration file in c:/Nn/default.xml, but I still get this error

Can you help me what is wrong with the code? Did I put the file in the wrong path?

int main(int argc, char* argv[])
{
help();
Settings s; 
const string inputSettingsFile = argc > 1 ? argv[1] : "c:/Nn/default.xml";
FileStorage fs(inputSettingsFile, FileStorage::READ); // Read the settings
if (!fs.isOpened())
{
    cout << "Could not open the configuration file: \"" << inputSettingsFile << "\"" <<            endl; 
    return -1;
}
fs["Settings"] >> s; 
fs.release();                                         // close Settings file

if (!s.goodInput)
{
    cout << "Invalid input detected. Application stopping. " << endl;
    return -1;
}

vector<vector<Point2f> > imagePoints;
Mat cameraMatrix, distCoeffs;
Size imageSize;
int mode = s.inputType == Settings::IMAGE_LIST ? CAPTURING : DETECTION;
clock_t prevTimestamp = 0;
const Scalar RED(0,0,255), GREEN(0,255,0);
const char ESC_KEY = 27;