Incrementing by 1 in dynamic textfield


I have a movie with a dynamic textbox which has variable name :collide.

This registers collisions between 2 vehicles. I need to make it increment by one for each collision. I have following code which doesn’t work:

_root.onEnterFrame = function () {

if(car1_mc.hitTest(car2_mc) == true) {

	n = 1;
	collide = Number(n++);


Could anybody give me the correct code?

Thanks your assistance.