# -*- coding: utf-8 -*-
n = int(input())
H = [0] * n
M = [0] * n
h = [0] * n
m = [0] * n
for i in range(n):
    temp1,temp2 = list(input().split())
    H[i],M[i] = map(int,temp1.split(":"))
    h[i],m[i] = map(int,temp2.split(":"))

def timelen(h1,m1,h2,m2):
    m1 += h1 * 60
    m2 += h2 * 60
    m = m2 - m1
    if m < 0:
        m += 1440
    return m

ans = 0

for i in range(n):
    ans += timelen(H[i],M[i],h[i],m[i])

print(ans)