Hydra Syntax for Web Form ?

Hello.
I am about to try HYDRA but I wonder one thing.

To break the password of a web form (http-post-form) for example, I put a fake user name and a wrong password and just after validated I noticed the phrase following error :

"The username or password is incorrect You entered. Check to make safe your Caps Lock is off, and That you are using the proper username and password."

Using the following syntax HYDRA:

hydra -l admin -P dic.txt -f -V localhost http-post-form \
"/index.php:username=^USER^&password=^PASS^&login=LogIn:is incorrect"

I wonder if this syntax I want to use is right and especially whether the <failure string> "is incorrect" I put in syntax?

Or do I put all the error sentence ("The username or password is incorrect You entered. Check to make safe your Caps Lock is off, and That you are using the proper username and password.") as the <failure string> ???

thank you