# -*- coding:utf-8 -*-

if __name__ == "__main__":
	n = input()
	ans = 0
	for i in xrange(n):
		d1,d2 = raw_input().split()
		h1,m1 = map(int,d1.split(":"))
		h2,m2 = map(int,d2.split(":"))
		if m2 - m1 < 0:
			m2 += 60
			h2 -= 1
		dif_m = m2 - m1
		if h2 - h1 < 0:
			h2 += 24
		dif_h = h2 - h1
		ans += dif_m + dif_h * 60
	print ans