N = int(input())
minutes_total = 0

for i in range(N):
    time_get_up, time_go_to_bed = [s for s in input().split()]
    hours_go_to_bed, minutes_go_to_bed = [int(i) for i in time_get_up.split(':')]
    hours_get_up, minutes_get_up = [int(i) for i in time_go_to_bed.split(':')]

    if hours_go_to_bed > hours_get_up:
        hours_get_up += 24

    minutes_total += (hours_get_up * 60 + minutes_get_up) - (hours_go_to_bed * 60 + minutes_go_to_bed)

print(minutes_total)