#! ruby
# yukicoder My Practice
# author: Leonardone @ NEETSDKASU

N = gets.to_i

total_sleep = 0

N.times do
	
=begin
	# 正規表現
	m = /(?<h1>\d+):(?<m1>\d+) (?<h2>\d+):(?<m2>\d+)/.match(gets)
	t1 = m[:h1].to_i * 60 + m[:m1].to_i
	t2 = m[:h2].to_i * 60 + m[:m2].to_i
=end

	(h1,m1),(h2,m2)=gets.chomp.split.map{|x|x.split(':').map(&:to_i)}
	t1 = h1 * 60 + m1
	t2 = h2 * 60 + m2

	total_sleep += t2 - t1 + (t2 < t1 ? 24 * 60 : 0)
end

puts total_sleep