#include <cassert>
#include <stdexcept>
class Stock {
    int capacity_;
    int used_;
public:
    Stock(int capacity, int used) : capacity_(capacity), used_(used) {
        if (capacity < 0 || used < 0 || used > capacity)
            throw std::invalid_argument("invalid stock");
    }
    int used() const noexcept { return used_; }
    void reserve(int amount) {
        if (amount < 0) throw std::invalid_argument("negative amount");
        if (amount > capacity_ - used_) throw std::out_of_range("no capacity");
        used_ += amount;
    }
};
int main() {
    Stock s(10, 3);
    s.reserve(7);
    assert(s.used() == 10);
    bool rejected = false;
    try { s.reserve(1); } catch (const std::out_of_range&) { rejected = true; }
    assert(rejected && s.used() == 10);
    rejected = false;
    try { Stock invalid(2, 3); } catch (const std::invalid_argument&) { rejected = true; }
    assert(rejected);
    Stock copy = s;
    copy.reserve(0);
    assert(copy.used() == s.used());
}