from datetime import time

def main():
    num = int(input())
    total_min = 0
    for i in range(num):
        wakeup, bedtime = input().split()

        wakeup_hour, wakeup_min = wakeup.split(':')
        wakeup = time(int(wakeup_hour), int(wakeup_min))

        bedtime_hour, bedtime_min = bedtime.split(':')
        bedtime = time(int(bedtime_hour), int(bedtime_min))

        minutes = bedtime.minute - wakeup.minute
        if wakeup.hour == bedtime.hour:
            if minutes >= 0:
                total_min += minutes
            else:
                total_min += (24 * 60) + minutes
        elif wakeup.hour < bedtime.hour:
            if minutes >= 0:
                total_min += (60 * (bedtime.hour - wakeup.hour)) + minutes
            else:
                hours = bedtime.hour - wakeup.hour
                total_min += 60 * hours + minutes
        else:
            if minutes >= 0:
                hours = bedtime.hour - wakeup.hour + 24
                total_min += 60 * hours + minutes
            else:
                hours = bedtime.hour - wakeup.hour + 24
                total_min += 60 * hours + minutes

        #print()
        #print(total_min)
        #print()

    print(total_min)



if __name__ == '__main__':
    main()