n = int(input())

x = 0
for _ in range(n):
    t1, t2 = input().split()
    h1, m1 = map(int, t1.split(':'))
    h2, m2 = map(int, t2.split(':'))
    
    if h2*60 + m2 > h1*60 + m1:
        x += (h2*60 + m2) - (h1*60 + m1)
    else:
        x += (h2*60 + m2) - (h1*60 + m1) + 1440

print(x)