Date operator+(int days) {
        for (auto i = 0; i != days; ++i) {
            ++(*this);
        }
    }
Date operator-(int days) {
        for (auto i = 0; i != days; ++i) {
            --(*this);
        }
    }
int operator-(const Date &date2) {
        return days_from_begining - date2.days_from_begining;
    }