Automatically displaying unique ID number

Dear Experts,
I am not a programmer though I am preparing a XLSForm for data collection.
I caught in a trouble when developing the form. The problem I am facing is,
Automatic display of Household Identification Number in a box. For example,
Region Name: Barisal
District Name: Chandgaon
Cluster Name: Rahalia
Village Name: Pandgaon
Household Serial Number: 0012
Household Identification Number will be: 3 letter for Region Name-3 letter of District Name-3 letter of Cluster Name-3 letter of Village Name-Household Serial Number (will automatically display like: BAR-CHA-RAH-PAN-0012)
If anyone help to solve this issue to develop in XLSForm would be highly appreciated.

Best Regards,

S R Dhamai