N = int(input())

ans = 0

for i in range(N):
    go_to_bed, wake_up = input().split()
    
    go_to_bed_hour, go_to_bed_min = [int(x) for x in go_to_bed.split(":")]
    wake_up_hour, wake_up_min = [int(x) for x in wake_up.split(":")]

    correction_hour = 0
    correction_min = 0
    correction_hour_for_min = 0
    
    if(go_to_bed_hour > wake_up_hour):
        correction_hour = 24
    
    if(go_to_bed_min > wake_up_min):
        correction_min = 60
        correction_hour_for_min = -1

    ans = ans + (wake_up_hour - go_to_bed_hour + correction_hour) * 60 + wake_up_min + correction_min - go_to_bed_min + correction_hour_for_min * 60
print(ans)