import java.io.*;
import java.util.*;
import java.text.*;
import java.math.*;
import java.util.regex.*;

public class Solution {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int xCord = -1;
        int yCord = -1;
        boolean flag = true;
        for(int a0 = 0; a0 < n; a0++){
            int x = in.nextInt();
            int y = in.nextInt();
            if(xCord == -1){
                xCord = x;
                yCord = y;
                continue;
            }
            
            if(xCord != x){
                if(yCord != y){
                    System.out.println("NO");
                    flag = false;
                    break;
                }
            }
            
            if(yCord != y){
                if(xCord != x){
                    System.out.println("NO");
                    flag=false;
                    break;                        
                }
            }
            
            xCord = x;
            yCord = y;
        }
        
        if(flag){
            System.out.println("YES");
        }
    }
}