def cicles_per_excavar(d,emax):
    total = 0
    n = 0
    while total<d and emax > 0:
        n = n + 1
        metres = 6/(1 + 0.5*(n-1))
        total = total + metres
        emax = emax - metres
    if emax < 0:
        return -1
    else:
        return n