function country() {
      return '{"RU": 15, "US": 29, "CH": 67}';
    }

    function countryI (amount, from, to) {
      if (country) {
        try {
          let a = JSON.parse(country());
            return amount * a[from] * a[to];
      } catch(err) {
     console.log(err.name, err.message);
  }
}
}

console.log(countryI(79, 'RU', 'US'))