#!/bin/python3

import sys


n = int(input().strip())
p_x, p_y = None, None
status = ""
px,py = input().strip().split(' ')
px,py = [int(px),int(py)]
horiz = None
for a0 in range(n-1):
    x,y = input().strip().split(' ')
    x,y = [int(x),int(y)]
    if horiz is None:
        if x == px:
            horiz = True
        elif y == py:
            horiz = False
        else:
            status = "NO"
            break
    else:
        if (horiz and x != px) or (not horiz and y != py):
            status = "NO"
            break

if status == "":
    print("YES")
else:
    print("NO")