Hyper V Powershell - memorymaximumbytes does not accept input from read-host

Hi

I am trying to create a script which will copy a vhdx file and create a new vm using the hyperv cmdlets however I keep getting the following error message on the memorymaximumbytes

cannot bind parameter memorymaximumbytes. cannot convert value "4GB" to type "System.Int64". Error: "Input was not in correct format"

I have the 4GB value bound to a variable of $maxmem which is prompted for using the read-host cmdlet.

Any ideas on how I can get this working?

Thanks