I got this table with a built in calculator function that select from different parts of the `table` and adds every thing up at the end. But my problem is that if I hit one of the squares with letters inside of them instead of numbers, the calculator breaks, how do I fix it?

How do I make the first like containing information(car names) unclickable, and only the first 5 squares.
The table code :

```
 <table>
      <tr>
        <th bgcolor="b8cce4">Modell</td>
          <th>Trend</td>
            <th>Titanum</td>
              <th>Familiepakke</td>
                <th>Førerassistentpakke</td>
                  <th>Stilpakke</td>
                    <th>Sluttpris</td>
      </tr>
      <tr>
        <td bgcolor="b8cce4"><b>Kuga</b></td>
        <td>401000</td>
        <td>420000</td>
        <td>1000</td>
        <td>10200</td>
        <td>9200</td>
        <td>kr</td>
      </tr>
      <tr>
        <td bgcolor="b8cce4"><b>C-max</b></td>
        <td>320000</td>
        <td>335000</td>
        <td>1000</td>
        <td>9400</td>
        <td>3600</td>
        <td>kr</td>
      </tr>
      <tr>
        <td bgcolor="b8cce4"><b>Focus</b></td>
        <td>255000</td>
        <td>325000</td>
        <td>900</td>
        <td>12500</td>
        <td>9000</td>
        <td>kr</td>
      </tr>
      <tr>
        <td bgcolor="b8cce4"><b>Mondeo</b></td>
        <td>281000</td>
        <td>361000</td>
        <td>1100</td>
        <td>9900</td>
        <td>7200</td>
        <td>kr</td>
      </tr>

```

The script:

```
   (function() {
      var tds = document.querySelectorAll('tr td:not(:last-child)');
      for (var td in tds) {
        tds[td].addEventListener('click', function(evt) {
          evt.target.classList.toggle('selected');
          var total = 0;
          var parentTr = evt.target.parentNode;
          var selected = parentTr.querySelectorAll('.selected');
          for (var k in selected) {
            if (selected[k].innerText) {
              total += parseInt(selected[k].innerText);
            }
          }
          parentTr.querySelector('td:last-child').innerText = total;
        });
      }
    })();

```