using namespace std;

class Vector {
private:
    int * data;
    size_t vect_size;
    size_t capacity;
public:
    Vector() {
        data = new int[0];
        vect_size = 0;
        capacity = 0;
    };
    Vector(const Vector& input) {
        vect_size = input.vect_size;
        capacity = input.capacity;
        data = new int[vect_size];
        for (size_t i = 0; i < vect_size; ++i) {
            data[i] = input.data[i];
        }
    }
    Vector& operator=(const Vector& input) {
        vect_size = input.vect_size;
        capacity = input.capacity;
        delete [] data;
        data = new int[vect_size];
        for (size_t i = 0; i < vect_size; ++i) {
            data[i] = input.data[i];
        }
        return *this;
    }
    ~Vector() {
        delete [] data;
    }
    size_t size() {
        return vect_size;
    }
    int operator[](size_t i) {
        return data[i];
    }
    void push_back(int elem) {
        if (vect_size == capacity) {
            int * tmp = new int[vect_size];
            if (vect_size) {
                for (size_t i = 0; i < vect_size; ++i) {
                    tmp[i] = data[i];
                }
                delete [] data;
            }
            if (!capacity) {
                capacity = 1;
            }
            capacity *= 2;
            data = new int[capacity];
            for (size_t i = 0; i < vect_size; ++i) {
                data[i] = tmp[i];
            }
            if (vect_size) {
                delete [] tmp;
            }
        }
        data[vect_size] = elem;
        ++vect_size;
    }
    void pop_back() {
        --vect_size;
    }
};