import sys
import datetime
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

n = int(readline())
ans = 0
for i in range(n):
    s1, s2 = map(str, readline().decode().strip().split(" "))
    a, b = s1.split(":")
    c, d = s2.split(":")
    aa = int(a) * 60 + int(b)
    bb = int(c) * 60 + int(d)
    t = bb - aa
    if t < 0:
        t += 24 * 60
    ans += t
    
print(ans)