from datetime import datetime, timedelta
n = int(input())
ans = 0
for i in range(n):
    S, s = list(map(str, input().split(' ')))
    H,M = list(map(int,S.split(':')))
    h,m = list(map(int,s.split(':')))
    sleep_time = datetime(2020,1,1,H,M)
    wake_time = datetime(2020,1,1,h,m)
    if sleep_time > wake_time:
        wake_time += timedelta(hours=24)
    ans += (wake_time - sleep_time).seconds
print(ans//60)