import datetime

N = int(input())
sum = 0
for i in range(N):
    l = list(map(str, input().split()))
    l1 = list(map(int, l[0].split(":")))
    l2 = list(map(int, l[1].split(":")))
    if l1[0] > l2[0]:
        d1 = datetime.datetime(2018, 6, 6,hour = l1[0], minute = l1[1])
    else:
        d1 = datetime.datetime(2018, 6, 7,hour = l1[0], minute = l1[1])
    d2 = datetime.datetime(2018, 6, 7, hour = l2[0], minute = l2[1])
    sum += (d2-d1).seconds

print(sum//60)