N = int(input())
T = []
ST = []
ET = []
sleepHours = []
sleepMinute = []
ans = 0

for i in range(N):
    T.append(list(map(str, input().split())))
    ST.append(list(map(int, T[i][0].split(":"))))
    ET.append(list(map(int, T[i][1].split(":"))))

    if ST[i][0] > ET[i][0]:
        sleepHours.append((ET[i][0] +24) - ST[i][0])
    else:
        sleepHours.append(ET[i][0] - ST[i][0])

    if ST[i][1] > ET[i][1] and sleepHours[i] == 0:
        sleepMinute.append((ET[i][1] + 60) - ST[i][1])
        sleepHours[i] += 23
    elif ST[i][1] > ET[i][1]:
        sleepMinute.append((ET[i][1] + 60) - ST[i][1])
        sleepHours[i] -= 1
    
    else:
        sleepMinute.append(ET[i][1] - ST[i][1])    

    ans += sleepHours[i] * 60 + sleepMinute[i]

print(ans)