N=int(input())
ANS=0

for i in range(N):
    x,y=input().split()

    h,m=x.split(":")

    h2,m2=y.split(":")

    #print(h,m,h2,m2)

    h=int(h)
    m=int(m)
    h2=int(h2)
    m2=int(m2)

    a=h*60+m
    b=h2*60+m2

    if a<=b:
        ANS+=b-a
    else:
        ANS+=b+(24*60)-a

print(ANS)