cnt=0
day=60*24
for i in range(int(input())):
    hoge=input().split()
    a=hoge[0].split(':')
    b=hoge[1].split(':')
    c=int(a[0])*60+int(a[1])
    d=int(b[0])*60+int(b[1])
    if(c<d):
        #print(1,c,d,d-c)
        cnt+=d-c
    elif(c>d):
        #jprint(2,c,d,d+day-c)
        cnt+=d+day-c
print(cnt)