How to limit same answer in form

I have a form with dropdown choice

<select id="ubytovanie" name="ubytovanie">
        <option value="">  </option>
        <option value="1"> 1 </option>
        <option value="2"> 2 </option>
        <option value="3"> 3 </option>
        <option value="4"> 4 </option>
        <option value="5"> 5 </option>
        <option value="6"> 6 </option>
        <option value="7"> 7 </option>
        <option value="8"> 8 </option>
        <option value="9"> 9 </option>
        <option value="10"> 10 </option>
        <option value="11"> 11 </option>
        <option value="12"> 12 </option>
      </select>

In my form you can choose room number in which you would like to stay. But there can be only 6 people in one room, so I need to limit the option so max 6 people can choose same room number. After that, the option with room number would be disabled for other people filling out the form.

Is there a way to do this with JavaScript? Thanks for answer