($n,$m)=glob<>;
@a=(0,glob<>);
for(<>){
    ($u,$v)=glob<>;
    $$u{$a[$v]-$a[$u]}=1;
    $$v{$a[$u]-$a[$v]}=1;
}
for(1..$n){
    @a=sort{$a<=>$b}keys%$_;
    if(@a>1){
	if($a[1]<0||$a[-2]>0){
	    print"YES";
	    exit;
	}
    }
}
print"NO";