($n,$m)=glob<>;
@s=map[glob],<>;
for(@s){
	++$d[$a=$_->[0]];
	++$d[$b=$_->[1]];
	vec($e[$a],$b,1)=1;
	vec($e[$b],$a,1)=1;
	vec($h,$a,1)=1;
	vec($h,$b,1)=1;
}
for(0..$n-1){
	$c+=$d[$_]%2;
}
if($c>2){
	print"NO";
	exit;
}

sub f{
	my($a)=@_;
	if(!vec($g,$a,1)){
		vec($g,$a,1)=1;
		for(0..$n-1){
			if(vec($e[$a],$_,1)){
				f($_);
			}
		}
	}
}

f(0);
if($g!=$h){
	print"NO";
	exit;
}
print"YES";