N=int(raw_input())
ans=0
for i in range(N):
    before,after = raw_input().split()
    bh,bm=map(int,before.split(':'))
    ah,am=map(int,after.split(':'))
    ah+=24
    t=-(bh*60+bm)+(ah*60+am)
    t%=24*60
    ans+=t
print ans