$n=<>;
for$i(1..$n){
	($r1,$c1,$r2,$c2)=glob<>;
	push@{"$r1,$c1"},"$r2,$c2";
	push@{"$r2,$c2"},"$r1,$c1";
	$a{"$r1,$c1,$r2,$c2"}=1;
	$a{"$r2,$c2,$r1,$c1"}=1;
}

sub hoge1 {
	my($yx)=@_;
	@$yx=grep{$a{"$yx,$_"}}@$yx;
	if(@$yx==1){
		$z=pop@$yx;
		$a{"$yx,$z"}=0;
		$a{"z,$yx"}=0;
		hoge1($z);
	}
}

for$y(1..100){
	for$x(1..100){
		hoge1("$y,$x");
	}
}

sub hoge2 {
	my($yx)=@_;
	if(@$yx>2){
		$f=1;
	}
	my@t=@$yx;
	@$yx=();
	for(@t){
		hoge2($_);
	}
}

for$y(1..100){
	for$x(1..100){
		hoge2("$y,$x");
	}
}

print $f?NO:YES;