template <typename T, typename U, typename Iterator_T, typename Iterator_U>
vector<pair<T, U>> zip(Iterator_T a_first, Iterator_T a_last, Iterator_U b_first, Iterator_U b_last) {
    vector<pair<T, U>> res;
    auto a_it = a_first;
    auto b_it = b_first;
    for (; not (a_it == a_last) and not (b_it == b_last); ++a_it, ++b_it) {
        res.emplace_back(*a_it, *b_it);
    }
    return res;
}
template <typename T>
class ArithmeticIterator : bidirectional_iterator_tag {
public:
    using difference_type = ptrdiff_t;
    using value_type = T;
private:
    value_type value;
public:
    ArithmeticIterator(const T& value) : value(value) {}
    value_type operator*() const { return value; }
    ArithmeticIterator<T>& operator++() { ++value; return *this; }
    ArithmeticIterator<T>& operator--() { --value; return *this; }
    bool operator==(const ArithmeticIterator<T>& rhs) const { return value == rhs.value; }
};
template <typename T> vector<pair<int, T>> enumerate(const vector<T>& container) {
    return zip<int, T>(ArithmeticIterator<int>(0), ArithmeticIterator<int>(INT_MAX), container.begin(), container.end());
}