John is 35 years old and has just realized that he needs to start saving for retirement. He plans to retire at the age of 65 and wants to ensure that he has enough money to withdraw $6700 every month from his retirement savings account from the age of 65 until the age of 85. If his retirement account earns a return of 3.9% per year, compounded monthly, how much does he need to save every month, with the first deposit occurring at the end of the current month, to reach his retirement savings goal? Enter your answer to the nearest cent (two decimal places).