How do I create a recurring event occurring at the end of each month?

I have to submit my timesheets twice per month; first on the 16th and then at the end of the month. Since different months have different end days (28/29 on February, 30 & 31 every other month,) when I set it to repeat on the 31st it skips the months where the 31st does not occur.

How do I change it such that it repeats every month at the end of the month, without skipping?