import datetime as dt
n = int(input())
v = 0
for i in range(n):
    s1,s2 = input().split()
    s1_array = s1.split(":")
    s1_h = int(s1_array[0])
    s1_m = int(s1_array[1])
    s1_delta = dt.timedelta(hours=s1_h,minutes=s1_m)
    
    s2_array = s2.split(":")
    s2_h = int(s2_array[0])
    s2_m = int(s2_array[1])
    s2_delta = dt.timedelta(hours=s2_h,minutes=s2_m)
    
    #print(dt.timedelta(hours=24)-s1_delta)
    if s1_h<24 and s2_h<=s1_h:
        #print(((dt.timedelta(hours=24)-s1_delta).seconds+s2_delta.seconds)//60)
        v+=((dt.timedelta(hours=24)-s1_delta).seconds+s2_delta.seconds)//60
    else:
        v+=(s2_delta.seconds-s1_delta.seconds)//60
print(v)