def somma_liv_pari(A):
    return aux(A,0)


def aux(A,livello):
    if A is None:
        return 0

    if A.sx is None and A.dx is None:
        if livello % 2 == 0:
            return A.val
        return 0

    somma = 0
    if livello % 2 == 0:
            somma = A.val

    if A.sx is not None:
        somma += aux(a.sx,livello + 1)

    if A.dx is not None:
        somma += aux(a.dx,livello + 1)

    return somma