What's the password, how to fix it?

What's the password?
/*****************************
* login.php Login Verification Processing file
*****************************/
Session_Start ();
Log Off Login
if ($_get[' action '] = = ' logout ') {
Session_unregister ("username");
Exit (');
}

If logged in is detected, jump directly to the admin page
if (isset ($_session[' username ')) {
Header ("location:http://". $_server[' Http_host '].rtrim (dirname ($_server[' php_self ']), '/\\ '). " /admin.php ");
Exit
}
if ($_post) {
Require ("./conn.php");
$username = $_post[' username ');
$password = MD5 (Trim ($_post[' password '));
$check _result = mysql_query ("Select UID from user WHERE username = ' $username ' and password = ' $password '");
if (mysql_fetch_array ($check _result)) {
Session_register ("username");
Header ("location:http://". $_server[' Http_host '].rtrim (dirname ($_server[' php_self ']), '/\\ '). " /admin.php ");
Exit
} else {
Echo ';
}
}

?>





<title>Message Management Login</title>









------Solution--------------------
$password = MD5 (Trim ($_post[' password '));

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