auto calculate total value
<p>i have form as shown in picture</p>

<p><img src="http://i.stack.imgur.com/kSYcR.jpg" alt="enter image description here"></p>

<p>what i need is, when i type/ change value in amount, it auto calculate sum at the bottom</p>

<p>also i don't want to let add any character...</p>

<p>Thanks</p>
