how to access multiple checkboxes names while checkbox name is coming from database in php

Below code is showing some data from database, here in each row there is a checkbox having name of primaryid from database ..and when user click less than then 5 checkboxes a alert appear as show all the code is working .but

Here I want that when user click 5 checkboxes i want the unique name of 5 checkboxes select and on submit button click and i want to do some php code with these 5 unique ids.

$sql="some sql";
$result = mysqli_query($mysql,$sql);

while($res1=mysqli_fetch_array($result,MYSQLI_ASSOC)) {


                    ?>
                                <tr>

                                <td>

                                <input type="checkbox" name="studentid"  value="<?php echo $res1['leadID']?>" ></td>


                <td>some stuff here </td>
                              </tr>
                    <?php }
                                ?>     

<input type="submit" name="submit" value="Submit" class="btn newcol1" id="submit2"  onClick="checkboxes();">


                 <script>
     function checkboxes()
      {

       var inputElems = document.getElementsByTagName("input"),
        count = 0;

        for (var i=0; i<inputElems.length; i++) {       
           if (inputElems[i].type == "checkbox" && inputElems[i].checked == true){
              count++;

           }

        }
        if(count < 5){
                  alert ("Select at least 5 leads");
                  }




  } </script>