class List {
public:
    List() {
        head = nullptr;
        tail = nullptr;
        size_of_list = 0;
    }

    ~List() {

    }

    void push_back(string data) {
        Node *new_element = new Node(data);
        if(size_of_list == 0) {
            head = new_element;
            tail = new_element;
        } else {
            tail->pNext = new_element;
            new_element->pPrev = tail;
            tail = new_element;
        }
        size_of_list++;
    }

    void push_front(string data) {
        Node *new_element = new Node(data);
        if(size_of_list == 0) {
            head = new_element;
            tail = new_element;
        } else {
            head->pPrev = new_element;
            new_element->pNext = head;
            head = new_element;
        }
        size_of_list++;
    }
private:
    class Node {
    public:
        Node *pPrev;
        Node *pNext;
        string data;

        Node(string data, Node *pPrev = nullptr, Node *pNext = nullptr) {
            this->data = data;
            this->pPrev = nullptr;
            this->pNext = nullptr;
        }
    };

    Node *head;
    Node *tail;
    int size_of_list;
};