Syntax Error 5

I really am trying to comb through the posts before asking questions, but I really can't figure out what is wrong.

var C5= this.getField("C5").value

if(((C5-3)/2)<0);

{

event.value=0;

}else{

event.value=((C5-3)/2);

}

It keeps giving me a syntax error 5

I am using Acrobat to create the form.