import re
n = int(input())
time = [list(map(int,re.split(r"[:\s]",input()))) for _ in range(n)]
total = 0
for t in time:
    if t[0] > t[2]:
        sleep = 1440 - (60*t[0]+t[1]) + (60*t[2]+t[3])
    elif t[2] == 0 and t[3] == 0:
        sleep = 1440 - (60*t[0]+t[1])
    else:
        sleep = (60*t[2]+t[3]) - (60*t[0]+t[1])
    total += sleep
print(total)