void task3()
{
    int k, count = 0;
    struct Stack *beforeLast = NULL;
    scanf("%d", &k);

    run = L;
    while (run->next != NULL) {
        if (run->next->inf == k) {
            ++count;
            beforeLast = run;
        }
        run = run->next;
    }

    if (count > 0) {
        run = beforeLast->next;
        beforeLast->next = beforeLast->next->next;
        free(run);
    }
}