@n=0..<>;
@s=map[glob],<>;
for(@s){
	$d[$a=$_->[0]]^=1;
	$d[$b=$_->[1]]^=1;
	vec($e[$a],$b,1)=vec($e[$b],$a,1)=1;
	$h|=$e[$a]|$e[$b]
}
sub f{
	my$e=$e[$_];
	$_||${$_=1;vec($e,$_,1)&&f()for@n}for vec$g,$_,1
}
f$_=$a;
print$g ne$h|grep($_,@d)>2?NO:YES