N = int(input())
ans = 0
for _ in range(N):
    L = list(input().split())
    H,M = L[0].split(':')
    h,m = L[1].split(':')
    H,M,h,m = int(H),int(M),int(h),int(m)
    M += H * 60
    m += h * 60
    if M > m:
        m += 24 * 60
    ans += m - M
print(ans)