from datetime import datetime, timedelta


def main():
    all_asleep_time = timedelta(minutes=0)
    for _ in range(int(input())):
        sleep, getup = input().split()
        sleep_h, sleep_m = map(int, sleep.split(":"))
        getup_h, getup_m = map(int, getup.split(":"))
        sleep_time = datetime(2022, 10, 28, sleep_h, sleep_m)
        getup_time = datetime(2022, 10, 28, getup_h, getup_m)

        if sleep_time < getup_time:
            all_asleep_time += (getup_time - sleep_time)
        else:
            all_asleep_time += timedelta(hours=24) - (sleep_time - getup_time)

    print(all_asleep_time // timedelta(minutes=1))


if __name__ == "__main__":
    main()