#!/bin/python
n = input()
x = 0
y = 0
matching = 0
result = True
for i in xrange(n):
    point = map(int, raw_input().split())
    if result == False:
        break;
    if i == 0:
        x = point[0]; y = point[1]
    elif i == 1:
        if point[0] == x and point[1] == y:
            continue
        if point[0] == x:
            matching = 0
        elif point[1] == y:
            matching = 1
        else:
            result = False
            break
    else:
        if matching == 0:
            if point[0] != x:
                result = False
                break
        if matching == 1 and point[1] != y: 
            result = False
            break;
if result:
    print 'YES'
else:
    print 'NO'