Trying to find the "Web application url" for stsadm tool

stsadm -o setsiteuseraccountdirectorypath -path <Valid OU name> –url <Web application URL>

I'm first trying to run stsadm -o getsiteuseraccountdirectorypath -url <Web application URL> to verify what is there currently, but no matter what URL I put in there, I get

"There is no top-level Web sit named xxxxxxxxxxxxxxx"

I have also checked the Central Administration --> Manage Web Applications and tried all the URLS listed there with no luck

Can anyone tell me how I can determined this value so I can execute that GET command?

thanks