tempalte<typename T>
class MyList{
private:
    struct Elem {
        T value;
        Elem* forward_ptr = nullptr;
        Elem* back_ptr = nullptr;
    };
    size_t size = 0;
    Elem* first = nullptr;
    Elem* last = nullptr;

public:
    void Push_back(const T& new_val) {
        Elem* in= new Elem{new_value, nullptr, nullptr};
        if (size == 0) {
            first = in;
        } else {
            last.forward_ptr = in;
            in.back_ptr = last;
        }
        last = in;
        ++size;
    }
    T Pop_back() {
        T temp = last->value;
        if (size == 1) {
            delete first;
            first = last = nullptr;
        } else {
            last->back_ptr->forward_ptr = nullptr;
            Elem* tempPtr = last;
            last = last->back_ptr;
            delete tempPtr;
        }
        --size;
        return temp;
    }
};