struct ElemStos
{
    double dane;
    ElemStos* next;
    ElemStos* prev;
};

ElemStos* push(ElemStos* stos,double wartosc)
{
    stos ->dane = wartosc;
    stos ->next = new ElemStos();
    stos -> next -> prev = stos;
    stos = stos->next;
    return stos;
}

ElemStos* pop(ElemStos* stos)
{
    if(stos != NULL)
    {
        if(stos -> prev != NULL)
        {
            stos = stos -> prev;
            delete(stos -> next);
            stos ->next = NULL;
        }
        else
        {
            delete(stos);
            stos = NULL;
        }
    }
    else
    {
        cout<<"Stos pusty";
        return stos;
    }
    return stos;
}

double top(ElemStos* stos)
{
    if(stos->prev==NULL)
    {
        return 0;
    }
    return stos->prev->dane;
}

bool empty(ElemStos* stos)
{
    if(stos == NULL || stos->prev==NULL)
    {
        return true;
    }
    return false;
}

typedef ElemStos* WskStos;