Formula to get the last date(30th or 31st) of the added month to a date in SharePoint calculated column

I have a column name DateOfJoining and another column EndProbation. When Date is filled in DateOfJoining Field (Eg: 5th June 2016) the last date of the 6th month added should be displayed in the EndProbation(Calculated column) column.(Eg: When 6 month is added it will be 5thDec but it should be 31st December). Please help me out to write Formula in calculated column.

Thanks in Advance.