Error message in if statement - reg

Dear Sir,

For the below said formula in excel, i am getting the error mentioned below, please do the needful.
Thanks in advance.

=IF(AF6="-","-",(AF6="","",IF(AF6<0.005,50,IF(AF6<0.0075,40,IF(AF6<0.01,30,IF(AF6<0.025,20,IF(AF6<0.05,3,IF(AF6<0.1,-10,IF(AF6>=0.1,-20)))))))))


Error Message:
The formula you typed contains an error.

> For information about fixing common formula problems , click help.
> To get assistance in entering a function , click ok , then click function on the insert menu
> If you are not trying to enter a formula, avoid using an equal (=) or minus sign (-), or precede it with a single quotation mark (').

You also missed an IF - you had: =IF(AF6="-","-",(AF6="","",IF(AF6<0.005,50,IF(AF..............
instead of: =IF(AF6="-","-",IF(AF6="","",IF(AF6<0.005,50,IF(AF....................