PHP Decode

</body> 
</html> 
         <?php 
            $msg = ''; 
 
            function gen_random() {  
               $a = rand(1337,2600)*33; 
               $b = rand(2424,3543)*33; 
 
               return $a+$b; 
            } 
 
            function hash_func($plain) { // md5 is the best LOL 
               $secured_plain = check_input($plain); 
               return md5($secured_plain); 
            } 
 
            function check_input($input) { // don't trust user 
               $re = '/[^a-zA-Z0-9]/'; 
               $secured_input = preg_replace($re, "", $input); 
               return $secured_input; 
            } 
             
            require_once "secret.php"; 
 
             
 
               $username = check_input($_POST['username']); 
               $password = hash_func($_POST['password']); 
               $rand = gen_random(); 
 
               //echo "user+rand==".$username.$rand ; 
               //echo "<br>"; 
               //echo "password==".$password; 
 
               if($username != true && $password != true) { 
                  if($username.$rand == $password) { 
                      
                   
                     echo 'You have entered valid usename and password'; 
                     echo nl2br("
Well, Your flag is : " . $flag); 
                                
                  } 
                  else { 
                     $msg = 'Wrong username or password'; 
                     echo $msg; 
                  } 
               } 
               else { 
                  $msg = 'Check your input again ... '; 
                  echo $msg; 
               } 
             
         ?>