void push__back(int x){
        point *q, *r;
        q = new point;
        q->el = x;
        q->link = nullptr;

        if (p == nullptr) {
            p = q;
            return;
        }

        r = p;
        int k = 0;
        while (p != nullptr) {
            k ++;
            p = p->link;
        }
        p->link = q;
        p = r;
    }