Powershell Create unqiue AD users by adding ascending number to samaccountname

Hi,

The company I'm working  at has a username policy: 2 first characters Givenname + 2 first characters Surname + ##
Example: John Smith will be given username josm01

I have this script that creates users. A part of the script defines samaccountname:

$sam = $_.Givenname.substring(0,2).ToLower() + $_.Lastname.substring(0,2).ToLower() + "01"
        Try   { $exists = Get-ADUser -LDAPFilter "(sAMAccountName=$sam)" }
        Catch { }
        If(!$exists)

Select allOpen in new window

If the username does not exist, the user is created.
If the username DOES exist, a line is written to a logfile and the creation of that user is cancelled.

I would like to have an adaption to the script:
If the username is found, the 01 is incremented by 1, to 02, or to the first available number.

Thanks in advance