N = int(input())
time = 0

for i in range(N):
    S1, S2 = map(str, input().split())
    H, M = map(int, S1.split(":"))
    h, m = map(int, S2.split(":"))

    if H > h or (H == h and M > m):
        h += 24

    time += h*60 + m - (H*60 + M)
    
print(time)