variables - Where is the error? (Basic Actionscript 2.0) -

so making extremely basic application on as2.0 reason, can't it. consists of 2 textboxes, (variables named "num1" , "num2") equal sign converted button (variable named "btn") , final textbox (variable named "res") show result of adding 2 numbers, ones given in "num1" , "num2" textboxes. here's i've tried:

on(click) { number(num1) + number(num2) = res; } 

i've tried

on(click) { number(num1) + number(num2) = res.text; } 

but none of seem work. 1 of these throw "nan" @ "res" textbox , other 1 throws out nothing. where's problem?

on(click) {     _root.res.text = number(_root.num1.text) + number(_root.num2.text); }