#!/bin/ruby

n = gets.chomp.to_i

els = []
first = nil
last = nil

n.times do |i|
  nums = gets.chomp.split(" ").map(&:to_i)
  first = nums.first
  last = nums.last
  els.push(nums)
end

if els.all?{|el| el.first == first } || els.all?{|el| el.last == last }
  puts "YES"
else
  puts "NO"
end