/* src/app.js */
app.get('/numbers/add/:a/and/:b', (req, res) => {
  const a = parseInt(req.params.a, 10);
  const b = parseInt(req.params.b, 10);

  return Number.isNaN(a) || Number.isNaN(b)
    ? res.sendStatus(400)
    : res.status(200).json({ result: add(a, b) });
});