Show sum of values for all checkboxes that are checked

I’m creating an HTML form and want to achieve the following with JS, please provide the code i should use to do so.

1.Add values of all the checked checkboxes and show them as total.

2.Add a restriction the user must select at least 2 checkboxes. Here is my code.

<input class="iput" type="checkbox" name="E33" value="4500" />
<input class="iput" type="checkbox" name="E34" value="3000" />
<input class="iput" type="checkbox" name="E36" value="6000" />

<p>Your Total is = </p>

Also code should be such that if i add or remove checkboxes i should not have to modify the JS code too.