public static int sommaPari(Albero a, int liv) {

    int somma = 0;

    if (liv % 2 == 0) {
        somma += a.val();
    }

    if (a.sx() != null) {
        somma += sommaPari(a.sx(), liv+1);
    }

    if (a.dx() != null) {
        somma += sommaPari(a.dx(), liv+1);
    }

    return somma;

}