def calc_max_holiday(calender: str) -> int:
    return max(map(len, calender.split("x")))


def main():
    D = int(input())
    calender = input()
    calender += input()
    calender = "x"*D + calender + "x"*D

    maximum = -1
    for idx in range(len(calender)):
        work_calender = calender
        next_holiday_idx = work_calender.find("o", idx)
        if next_holiday_idx == -1:
            paid_holiday = min(D, len(work_calender)-idx)
            work_calender = work_calender[:idx] + "o" * \
                paid_holiday + work_calender[idx+paid_holiday:]

        else:
            paid_holiday = min(next_holiday_idx - idx, D)
            work_calender = work_calender[:idx] + "o" * \
                paid_holiday + work_calender[idx+paid_holiday:]

        maximum = max(maximum, calc_max_holiday(work_calender))

    print(maximum)


if __name__ == "__main__":
    main()