N = int(input())
total = 0

for _ in range(N):
    HMhm = input().split()
    H, M = HMhm[0].split(':')
    h, m = HMhm[1].split(':')
    
    h1 = int(H) * 60 + int(M)
    h2 = int(h) * 60 + int(m)

    if h1 > h2:
        h1 = 1440 - h1
        total += h1 + h2
    else:  
        total += h2 - h1
    
print(total)