Problemer med count(*)

You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '-20,23' at line 1

PHP kode 

 $getnummessages = "SELECT COUNT(*) AS messagecount FROM chatmessages";
 $getnummessages2 = mysql_query($getnummessages) or die("blah");
 $getnummessages3 = mysql_result($getnummessages2, 0);
 
 if($getnummessages3>21)
 {
 
    $startrow = $getmessages3-20;
 }
 else
 {
   $startrow = 1;
 }