Abr __23_06_2016(Abr t, int k){
    if(t){
        if(t->key < k)
            t->dx = __23_06_2016(t->dx, k);
        else if(t->key > k)
            t->sx = __23_06_2016(t->sx, k);
    }
    else{
        t = (Abr)malloc(sizeof(albero));
        t->key = k;
        t->sx = t->dx = NULL;
    }
    return t;
}