N = int(input())

ans = 0

for i in range(N):
    
    hour = 0
    minitue = 0
    correct_hour = 0
    correct_min = 0

    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(":")]
    
    if go_to_bed_hour == 0:
        go_to_bed_hour = 24
    if wake_up_hour == 0:
        wake_up_hour = 24
    
    go_to_bed_min_time = go_to_bed_hour * 60 + go_to_bed_min
    wake_up_min_time = wake_up_hour * 60 + wake_up_min
    
    
    if wake_up_min_time > go_to_bed_min_time:
        ans = ans + wake_up_min_time - go_to_bed_min_time
    else:
        ans = ans + wake_up_min_time - go_to_bed_min_time + 1440
        
print(ans)