n = int(input())
sum = 0
for i in range(n):
    a, b = input().split()
    H, M = map(int, a.split(":"))
    h, m = map(int, b.split(":"))
    time = h-H
    if time < 0:
        time = 24 + time
    time = time * 60 + (m - M)
    sum+=time
    time = 0
print(sum)