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 a[]= new int[20];
        int flag=0;
        for(int a0 = 0; a0 < n; a0++){
            int x = in.nextInt();
            a[a0]=x;
            int y = in.nextInt();
            a[a0+1]=y;
        }
        for(int a0= 0; a0<n ; a0++ )
            {
            if((a[a0]==a[a0+2]) && a[a0+1]==(a[a0+3]-1))
                flag=1;
            else 
                flag=0;
        }
        if(flag==1)
        System.out.println("YES");
        else
            System.out.println("NO");
        
        
    }
}