IF syntax - user guide example doesn't work

IF syntax - user guide example doesn't work

Sorry if this is very basic, but I'm stuck when setting this up (I'm a very new user). For debugging simplicity, there is no other custom deluge code on the form (just a decision box, and a submit button). 

I'm trying to set up a conditional IF statement for the "on click" action of the button, that evaluates whether a decision box is checked. Taken straight from the user's guide, I set it up like this (substituting the name of the decision box on my form):

if ( (input.box== "false") )

alert "Please agree to the terms and conditions";
cancel submit ;
};

I get an error on line 1:

Error at line number : 1
Improper Statement
Error might be due to missing ';' at end of the line or incomplete expression