Due to lack of VB skills, most likely this stupid question

In Robotask, a report is being generated for the previous month. In short: {MonthNo} - 1 will do.
The report should be mailed, but instead of "Report of 10", ofcourse the best way is "Report of Oktober". (The report is generated in November). So: variable {MonthName} should be used.
Ofcourse, I cannot do {MonthName-1}. How can I make sure the name of the previous is being used?