Dynamic dice?

[--Fusiox--]

Hey, I'm trying to make a dice-rolling program that can change the amount of sides available, for a small demo. It's for a game I am developing just to see if I can, so I'm in no rush. This is my entire (and very short) source code:

stop();

dieSides = sidesInput; 
wepBonus = bonusInput;

btnRoll.onRelease = function(){
	die = Math.round(Math.random() * sidesInput);
             die += wepBonus;
} // end roll

As you can see, I have a dynamic text field named "sidesInput" and "bonusInput". I make the variable "dieSides" equal to the text field "sidesInput", as well with "wepBonus" and "bonusInput".

When I click the button "btnRoll", the text field "die" should become equal to a random number multiplied by "sidesInput" rounded to the nearest whole number, with the variable "wepBonus" added to the final result. In theory, this should work for me. But whenever I press "btnRoll" and start off the function that creates the output, all I get is an annoying "NaN" as the output.

How can I fix this?