c=0
for _ in range(int(input())):
    s,a=input().split()
    sH,sM=map(int,s.split(':'))
    aH,aM=map(int,a.split(':'))
    if aM<sM:aM+=60;aH-=1
    if aH<sH:aH+=24
    c+=(aH-sH)*60+aM-sM
print(c)