Help with cracking md5

Hi everyone, I'm new to the forums and to hashcat in general so forgive me if I ask any silly questions.

So basically I'm just trying to experiment a bit on my own and created a hash for hashcat to crack. Let's say the password is arsenal123 and I know that the password starts with arsenal but I don't know the rest of the numbers/letters. How can I input the arsenal portion of the password so that Hashcat doesn't have to go through those letters trying to crack it? I only want it to crack the last 3 characters of the password.

Thanks everybody