def fibitts(s_population: list, months: int, previous = None):
    #every 2 months: 1 pair -> 2 pairs
    #newborn pair can produce a new pair only after 2 months

    if previous is None:
        previous = s_population[0]

    for month in range(months+1):
        if month == 0:
            pass
        else:
            s_population.append(s_population[month]+previous)
            print(f"Month {month}: {s_population[month]}")
            previous = s_population[month]

fibitts([1,1], 24)