script code login Sql

<?php
include "config/koneksi.php";
if($_POST['login']){
$username=$_POST['username'];
$pass=$_POST['pass'];
$rs=mysql_query("select * from admin where username='$username'") or die(mysql_error());
if($rw=mysql_fetch_array($rs)){
if($s==$rw[password]){
$_SESSION['username']=$n;
$_SESSION['pass']=$rw[pass];
echo"<script>alert('sistem keamanan !!Anda Berhasil Login tahap 1');location='admin/index.php';</script>";
}else echo "Anda Memasukan Password Yang Salah!";
}else echo "Anda Memasukan Nama Yang Salah!";
}
?>