hs=ms=0
N=int(input())
for i in range(0, N):
    HhMm=input().split()
    H,M=map(int, HhMm[0].split(':'))
    h,m=map(int, HhMm[1].split(':'))
    hs+=(h-H)%24
    ms+=m-M
print(hs*60+ms)