Help needed with math.round function

Hi,

I have this piece of code :

[font=Times New Roman][size=3]var c4 = Math.sqrt ((c3*(1-c3)/(num1+num2))+(c3*(1-c3)/(num3+num4)));[/size][/font]
When I run my program I get values upto several decimals. How do I use the Math.round to the above piece of code to truncate to say 4 decimal places.

Please suggest.

Thanks.