N = int(input())

H = 0
M = 0
for _ in range(N):
    X, Y = input().split()
    H1, M1 = map(int, X.split(':'))
    H2, M2 = map(int, Y.split(':'))
    if H1 <= H2:
        H += H2 - H1
        M += M2 - M1
    else:
        H += (23 - H1) + H2
        M += (60 - M1) + M2

print(H*60 + M)