N=int(input())
ans=0
for _ in range(N):
    sleep,awake=input().split()
    sH,sM=map(int,sleep.split(':'))
    aH,aM=map(int,awake.split(':'))
#    print(sH,sM,aH,aM)
    
    if aH<sH:
        aH+=24
    if aM<sM:
        aM+=60
        aH-=1
#    print(aH-sH, aM-sM)
    ans+=(aH-sH)*60+aM-sM
print(ans)