N = int(input())

ans = 0

for i in range(N):
    
    HM, hm = input().split()
    
    H, M = map(int, HM.split(':'))
    
    h, m = map(int, hm.split(':'))
    
    ans += (h * 60 + m - H * 60 - M) % 1440
    
print(ans)