n = int(input())
ans = 0
for _ in range(n):
    hw0, hw1 = input().split()
    h0, w0 = hw0.split(":")
    h1, w1 = hw1.split(":")
    h0 ,h1, w0, w1 = int(h0), int(h1), int(w0), int(w1)
    ans += (h1 - h0) % 24 * 60 + (w1 - w0)
print(ans)