N = int(input())
H = [0] * N
M = [0] * N
h = [0] * N
m = [0] * N
time = 0

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

    if H[i] > h[i]:
        h[i] += 24

    time += h[i]*60 + m[i] - (H[i]*60 + M[i])

print(time)