Mr. Ng contributed $1000 to an RRSP at the beginning of each calendar quarter for the past 20 years. The plan earned 10% compounded quarterly for the first 10 years and 12% compounded quarterly for the last 10 years. He is converting the RRSP to a Registered Retirement Income Fund (RRIF) and intends to withdraw equal amounts at the beginning of each month for 15 years. If the funds in the RRIF earn 8.5% compounded monthly, what maximum monthly amount can be withdrawn?