n = int(input())
hour=0
time=0

for i in range(n):
    data = input().split()
    H,M = map(int,data[0].split(":"))
    h,m = map(int,data[1].split(":"))
    
    if h >= H:
        hour = h - H
    else:
        hour = 24-H + h
    
    if m>=M:
        min = m-M
    else:
        min = 60-M + m
        hour -= 1
    
    if hour<0:
        hour += 24
        
    time += hour*60 + min
    
print(time)