n = int(input())
minute = 0

for _ in range(n):
    time = list(map(int, input().replace(":" ," ").split()))
    tt1, tt2 = [h * 60 + m for h, m in zip(time[0::2], time[1::2])]
    minute += tt2 - tt1 if tt2 - tt1 > 0 else (tt2 + 24 * 60) - tt1

print(minute)