void DelEnd(node*& H)
{
    if (H != NULL)
    {
        node* P = H;
        if (P->next == NULL)
            DelNode(H);

        else
        {
            while (P->next->next != NULL)
                P = P->next;
            DelNode(P->next);

        }
    }
}

// Usuń co drugi
void Del2nd(node*& H)
{
    node* P = H;
    while (P && P->next)
    {
        DelNode(P->next);
        P = P->next;
    }
}

// Kopiuj parzyste elementy
void CopyEven(node* H)
{
    if (H != NULL)
    {
        node* P = H;
        while (P != NULL)
        {
            if (P->val % 2 == 0)
            {
                node* q = new node;
                q->val = P->val;
                q->next = P->next;
                P->next = q;
                P = q->next;
            }
            else
            {
                P = P->next;
            }
        }
    }
}

//12 Zamiana X z nastepnikiem
void ReplaceXandNext(node*& H, int x)
{
    node* P = H;
    if (H->val != x)
    {
        while (P->next != 0 && P->next->val != x)
        {
            P = P->next;
        }
        if (P->next != NULL && P->next->next != NULL)
        {
            node* q = P->next;

            P->next = q->next;
            q->next = P->next->next;
            P->next->next = q;
        }
    }
    else
    {
        H = H->next;
        P->next = H->next;
        H->next = P;
    }
}