Enumerating all AD users, so script runs in a loop

Question

I am going to do a SharePoint upgrade this weekend from 2010 to 2013.
I need this script to run against every Active Directory user automatically, not just one at a time. How do I get this get this script to do that? I figure I create a pipeline, I just don't know where.
Here is the script:
Param(
    [string]  $account = $(Read-Host -prompt "UserAccount")
Add-PSSnapIn Microsoft.SharePoint.PowerShell
foreach ($wa in get-SPWebApplication)
    Write-Host "$($wa.Name) | $($wa.UseClaimsAuthentication )"
    #http://technet.microsoft.com/en-us/library/gg251985.aspx
    $wa.UseClaimsAuthentication = $true
    $wa.Update()
    $account = (New-SPClaimsPrincipal -identity $account -identitytype 1).ToEncodedString()
    $zp = $wa.ZonePolicies("Default")
    $p = $zp.Add($account,"PSPolicy")
    $fc=$wa.PolicyRoles.GetSpecialRole("FullControl")
    $p.PolicyRoleBindings.Add($fc)
    $wa.Update()
    $wa.MigrateUsers($true)
    $wa.ProvisionGlobally()
Please help me! Thank you!

Answer 1

Thank you! 
Where would I place this line in the script?
SR
http://technet.microsoft.com/en-us/scriptcenter/dd793612.aspx
¯\_(ツ)_/¯