n = int(input())
total = 0
for _ in range(n):
    line = input().strip().split()
    sleep = list(map(int, line[0].split(':')))
    wake = list(map(int, line[1].split(':')))
    
    sleep_min = sleep[0] * 60 + sleep[1]
    wake_min = wake[0] * 60 + wake[1]
    
    if wake_min < sleep_min:
        total += (wake_min + 1440) - sleep_min
    else:
        total += wake_min - sleep_min
print(total)